Adopt b2b.next's client patterns: services, page state, feedback

Ported from the owner's b2b.next and adapted from MudBlazor to the daisyUI
components:
- LocalizableComponentBase provides CascadingState, Navigation, Toast,
  IsLoading/IsDefaultDisabled, WhenOnline/StartOnlinePolling, and after-render
  jobs that actually run.
- CascadingState starts with initialised state and polls the online status
  with a PeriodicTimer. It reports errors through ILoggingService plus a toast,
  and disposes what it holds.
- New pieces:
  - ToastService + ToastHost, the snackbar, with AddResponseError/Success/
    Warning/Exception in SUtility;
  - ErrorViewer, which shows the validation messages plus AdditionalError(s);
  - LoggingService, which writes to the console and the IndexedDB client log.
- HttpService is rebuilt and registered:
  - auth levels Get/Post/Delete, *Anon and *TotallyAnon;
  - retry with backoff;
  - classified failures (FailureCodes) instead of exceptions;
  - HTTP 410 on cancel;
  - the "default" client.
  ReadWebResult and DefaultReadFromJsonAsync read its responses.
- ClientJsonContext is source-generated, and SUtility.DefaultSerializer and
  Blazored.LocalStorage use it.
- WebResult gains a C# 14 IsInvalid extension property.

The code follows the imported rules:
- Every service and async helper takes a CancellationToken last.
- Primary constructors replace constructor-plus-fields.
- MessagesService and IStorage return Task<WebResult> / Task<List<T>>.
  MessagesService is still mock, building its results in memory; the seed
  feed and thread moved to Faker.
- Index and ExpandMessage follow the page pattern: an offline guard with
  WhenOnline, LoadData, and early returns with toasts on the results they used
  to ignore. ExpandMessage reloads on route change and shows "not found"
  instead of a null message.
- Model and state collections are [], and the fake identity defaults moved
  out of the models.
- Components:
  - no ?. chains over initialised state;
  - [Inject] instead of @inject;
  - IsDefaultDisabled on the actions;
  - autocomplete on every text input;
  - Localizer[key, args] instead of string.Format;
  - the localizer no longer leaks its inner _pLocalizer.
- Settings → General gains a language picker (English/Italiano), and
  SetDefaultCulture limits the culture to those two.

Bugs fixed along the way:
- A compose with untouched (null) content passed the empty check.
- File errors were joined with <br/> and rendered as markup.
- ClientLogs.ErrorMessage() threw on warnings.
- CoalescingStringLocalizer[key, args] showed a raw "{0}" for missing keys.
- AppStatusService exposed a call to a JS function that doesn't exist.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Models/BoostingUser.cs

@@ -2,10 +2,10 @@
 {
 	public class BoostingUser
 	{
-		public string UserId { get; set; } = "45f14fa8-c40f-4121-997c-ef2542196a50";
-		public string UserName { get; set; } = "@loosy@letsrulethe.world";
-		public string DisplayName { get; set; } = "loosy";
-		public string PictureUrl { get; set; } = "https://letsrulethe.world/media/ddd91d51-dc12-4b82-86a2-2a28cc959183/L51ZAL4QEL07";
-		public string ProfileUrl { get; set; } = "https://letsrulethe.world/users/loosy";
+		public string UserId { get; set; }
+		public string UserName { get; set; }
+		public string DisplayName { get; set; }
+		public string PictureUrl { get; set; }
+		public string ProfileUrl { get; set; }
 	}
 }

Models/ClientLogs.cs

@@ -7,21 +7,19 @@
 		public string WarningMessage { get; set; }
 		public ClientLogException Exception { get; set; }
 		public DateTime TimeStamp { get; set; } = DateTime.Now;
+		/// <summary>The entry as HTML for a log viewer: the warning text, or the exception's details.</summary>
 		public string ErrorMessage()
 		{
-			if (Exception.InnerExceptionMessage != null)
-			{
-				return @$"<b>Type</b>: {Exception.Type ?? "N/A"} <b>HelpLink</b>: {Exception.HelpLink ?? "N/A"} <b>HResult</b>: {Exception.HResult ?? "N/A"}<br>
-<b>Source</b>: {Exception.Source ?? "N/A"} <b>StackTrace</b>: {Exception.StackTrace ?? "N/A"} <b>MemberName</b>: {Exception.TargetSiteName ?? "N/A"}<br>
-<b>Message</b>: {Exception.Message ?? "N/A"}<br>
-<b>InnerExceptionMessage</b>:{Exception.InnerExceptionMessage ?? "N/A"}";
-			}
-			else
-			{
-				return @$"<b>Type</b>: {Exception.Type ?? "N/A"} <b>HelpLink</b>: {Exception.HelpLink ?? "N/A"} <b>HResult</b>: {Exception.HResult ?? "N/A"}<br>
+			if (Exception is null)
+				return WarningMessage;
+
+			var details = @$"<b>Type</b>: {Exception.Type ?? "N/A"} <b>HelpLink</b>: {Exception.HelpLink ?? "N/A"} <b>HResult</b>: {Exception.HResult ?? "N/A"}<br>
 <b>Source</b>: {Exception.Source ?? "N/A"} <b>StackTrace</b>: {Exception.StackTrace ?? "N/A"} <b>MemberName</b>: {Exception.TargetSiteName ?? "N/A"}<br>
 <b>Message</b>: {Exception.Message ?? "N/A"}";
-			}
+			if (Exception.InnerExceptionMessage is null)
+				return details;
+
+			return $"{details}<br>\n<b>InnerExceptionMessage</b>:{Exception.InnerExceptionMessage}";
 		}
 	}
 

Models/FailureCodes.cs

@@ -0,0 +1,20 @@
+namespace decePubClient.Models;
+
+/// <summary>
+/// WebResult.ErrorCode values HttpService sets when a request fails before or outside the server, so the UI can tell a
+/// connectivity problem (shown as a warning) from a real error.
+/// </summary>
+public static class FailureCodes
+{
+	public const string Cancelled = "CANCELLED";
+	public const string DeviceOffline = "DEVICE-OFFLINE";
+	public const string Timeout = "TIMEOUT";
+	public const string ApiUnreachable = "API-UNREACHABLE";
+	public const string RetriesExhausted = "RETRIES-EXHAUSTED";
+	public const string ServerError = "SERVER-ERROR";
+	public const string ClientError = "CLIENT-ERROR";
+	public const string Unauthorized = "UNAUTHORIZED";
+
+	public static bool IsConnectivity(string errorCode) =>
+		errorCode is DeviceOffline or Timeout or ApiUnreachable or RetriesExhausted;
+}

Models/Media.cs

@@ -6,6 +6,6 @@
 		public string Url { get; set; }
 		public string ContentType { get; set; }
 		public string AltText { get; set; }
-		public byte[] Blob { get; set; } //TODO TEMPORARY
+		public byte[] Blob { get; set; } = []; //TODO TEMPORARY
 	}
 }

Models/Message.cs

@@ -16,7 +16,7 @@ namespace decePubClient.Models
 		public int BoostsCounter { get; set; } = 0;
 		public bool IsBoostedByCurrentUser { get; set; } = false;
 		public BoostingUser BoostingUser { get; set; }
-		public List<Media> Medias { get; set; } = new();
+		public List<Media> Medias { get; set; } = [];
 		public DateTime CreatedAt { get; set; }
 
 		[Bindable(false), JsonIgnore]

Models/MessageForm.cs

@@ -19,7 +19,7 @@ public class MessageForm
 	public string Title { get; set; }
 	[StringLength(5_000, ErrorMessageResourceName = ValidationNames.MaxLength, ErrorMessageResourceType = typeof(ErrorMessages))]
 	public string Content { get; set; }
-	public List<UploadMedia> Media { get; set; } = new();
+	public List<UploadMedia> Media { get; set; } = [];
 
 	[JsonIgnore, Bindable(false)]
 	public MediaType MediaType { get; set; } = MediaType.Images;

Models/MessageUser.cs

@@ -2,11 +2,11 @@
 {
 	public class MessageUser
 	{
-		public string UserId { get; set; } = "45f14fa8-c40f-4121-997c-ef2542196a50";
-		public string UserName { get; set; } = "@loosy@letsrulethe.world";
-		public string DisplayName { get; set; } = "loosy";
-		public string PictureUrl { get; set; } = "https://letsrulethe.world/media/ddd91d51-dc12-4b82-86a2-2a28cc959183/L51ZAL4QEL07";
-		public string BackgroundUrl { get; set; } = "https://letsrulethe.world/media/9a3cc6c4-1018-4f41-86c7-f3e63e362bf4/EXM8RUK10B0Z";
-		public string ProfileUrl { get; set; } = "https://letsrulethe.world/users/loosy";
+		public string UserId { get; set; }
+		public string UserName { get; set; }
+		public string DisplayName { get; set; }
+		public string PictureUrl { get; set; }
+		public string BackgroundUrl { get; set; }
+		public string ProfileUrl { get; set; }
 	}
 }

Models/PublicCacheData.cs

@@ -6,12 +6,12 @@ namespace decePubClient.Models
 {
 	public class PublicCacheData
 	{
-		public IReadOnlyList<ViewLanguage> Languages { get; set; } = new List<ViewLanguage>();
-		public List<MediaDeviceInfo> QrCodeDevices { get; set; } = new();
+		public IReadOnlyList<ViewLanguage> Languages { get; set; } = [];
+		public List<MediaDeviceInfo> QrCodeDevices { get; set; } = [];
 		public string LastPage { get; set; }
 		public string CurrentSubPage { get; set; }
 		public PageSettings PageSettings { get; set; } = new();
 		public bool ShowLogs { get; set; } = false;
-		public IReadOnlyDictionary<string, string> Policies { get; set; } = new ReadOnlyDictionary<string, string>(new Dictionary<string, string>());
+		public IReadOnlyDictionary<string, string> Policies { get; set; } = ReadOnlyDictionary<string, string>.Empty;
 	}
 }

Models/UploadMedia.cs

@@ -8,7 +8,7 @@ public class UploadMedia
 	public string ContentType { get; set; }
 	public string FileName { get; set; }
 	public string AltText { get; set; }
-	public byte[] Blob { get; set; }
+	public byte[] Blob { get; set; } = [];
 
 	[JsonIgnore, Bindable(false)]
 	public string Base64Preview { get; set; }

Models/User.cs

@@ -2,15 +2,34 @@
 {
 	public class User
 	{
-		public string Id { get; set; } = "45f14fa8-c40f-4121-997c-ef2542196a50";
+		public string Id { get; set; }
 		public bool IsAuthenticated { get; set; } = false;
-		public List<UserClaim> Claims { get; set; } = new();
+		public List<UserClaim> Claims { get; set; } = [];
 		
-		public string UserName { get; set; } = "@loosy@letsrulethe.world";
-		public string DisplayName { get; set; } = "loosy";
-		public string PictureUrl { get; set; } = "https://letsrulethe.world/media/ddd91d51-dc12-4b82-86a2-2a28cc959183/L51ZAL4QEL07";
-		public string BackgroundUrl { get; set; } = "https://letsrulethe.world/media/9a3cc6c4-1018-4f41-86c7-f3e63e362bf4/EXM8RUK10B0Z";
-		public string ProfileUrl { get; set; } = "https://letsrulethe.world/users/loosy";
+		public string UserName { get; set; }
+		public string DisplayName { get; set; }
+		public string PictureUrl { get; set; }
+		public string BackgroundUrl { get; set; }
+		public string ProfileUrl { get; set; }
+
+		public MessageUser ToMessageUser() => new()
+		{
+			UserId = Id,
+			UserName = UserName,
+			DisplayName = DisplayName,
+			PictureUrl = PictureUrl,
+			BackgroundUrl = BackgroundUrl,
+			ProfileUrl = ProfileUrl
+		};
+
+		public BoostingUser ToBoostingUser() => new()
+		{
+			UserId = Id,
+			UserName = UserName,
+			DisplayName = DisplayName,
+			PictureUrl = PictureUrl,
+			ProfileUrl = ProfileUrl
+		};
 	}
 
 	public class UserClaim

Models/ValidationErrors.cs

@@ -0,0 +1,11 @@
+namespace decePubClient.Models;
+
+/// <summary>ASP.NET Core's validation ProblemDetails, as the server returns it for an invalid request body.</summary>
+public class ValidationErrors
+{
+	public string Type { get; set; }
+	public string Title { get; set; }
+	public int Status { get; set; }
+	public Dictionary<string, string[]> Errors { get; set; } = [];
+	public string TraceId { get; set; }
+}