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

Services/CoalescingStringLocalizer.cs

@@ -6,50 +6,59 @@ using PrivaPub.ClientModels.Resources;
 
 namespace collAnon.Client.Services
 {
-	public sealed class CoalescingStringLocalizer
+	/// <summary>
+	/// The app's localizer: looks a key up in Resources/AllStrings, then in PrivaPub.ClientModels' FieldsNameResource and
+	/// ErrorsResource, and falls back to the key itself (formatted with the arguments), so a missing key shows its
+	/// English text instead of failing.
+	/// </summary>
+	public sealed class CoalescingStringLocalizer(IStringLocalizer<AllStrings> baseLocalizer, IStringLocalizer<FieldsNameResource> fieldsLocalizer,
+		IStringLocalizer<ErrorsResource> errorsLocalizer)
 	{
-		public readonly IStringLocalizer<AllStrings> _pLocalizer;
-		readonly IStringLocalizer<FieldsNameResource> _fLocalizer;
-		readonly IStringLocalizer<ErrorsResource> _eLocalizer;
+		public IStringLocalizer Base => baseLocalizer;
+		public IStringLocalizer Fields => fieldsLocalizer;
+		public IStringLocalizer Errors => errorsLocalizer;
 
-		public CoalescingStringLocalizer(
-		IStringLocalizer<AllStrings> pLocalizer,
-		IStringLocalizer<FieldsNameResource> fLocalizer,
-		IStringLocalizer<ErrorsResource> eLocalizer) =>
-			(_pLocalizer, _fLocalizer, _eLocalizer) =
-			(pLocalizer, fLocalizer, eLocalizer);
-
-		internal LocalizedString this[string name]
+		public LocalizedString this[string name]
 		{
 			get
 			{
-				if (_pLocalizer[name].ResourceNotFound)
-					if (_fLocalizer[name].ResourceNotFound)
-						if (_eLocalizer[name].ResourceNotFound)
-							return new(name, name, false);
-						else
-							return _eLocalizer[name];
-					else
-						return _fLocalizer[name];
-				else
-					return _pLocalizer[name];
+				try
+				{
+					if (!baseLocalizer[name].ResourceNotFound)
+						return baseLocalizer[name];
+					if (!fieldsLocalizer[name].ResourceNotFound)
+						return fieldsLocalizer[name];
+					if (!errorsLocalizer[name].ResourceNotFound)
+						return errorsLocalizer[name];
+					return new(name, name, true);
+				}
+				catch (Exception ex)
+				{
+					Console.WriteLine(ex.ToString());
+					return new(name, name, true);
+				}
 			}
 		}
 
-		internal LocalizedString this[string name, params object[] arguments]
+		public LocalizedString this[string name, params object[] arguments]
 		{
 			get
 			{
-				if (_pLocalizer[name].ResourceNotFound)
-					if (_fLocalizer[name].ResourceNotFound)
-						if (_eLocalizer[name].ResourceNotFound)
-							return new(name, name, false);
-						else
-							return _eLocalizer[name, arguments];
-					else
-						return _fLocalizer[name, arguments];
-				else
-					return _pLocalizer[name, arguments];
+				try
+				{
+					if (!baseLocalizer[name].ResourceNotFound)
+						return baseLocalizer[name, arguments];
+					if (!fieldsLocalizer[name].ResourceNotFound)
+						return fieldsLocalizer[name, arguments];
+					if (!errorsLocalizer[name].ResourceNotFound)
+						return errorsLocalizer[name, arguments];
+					return new(name, string.Format(name, arguments), true);
+				}
+				catch (Exception ex)
+				{
+					Console.WriteLine(ex.ToString());
+					return new(name, name, true);
+				}
 			}
 		}
 	}