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

LayerComponents/LocalizableComponentBase.cs

@@ -1,12 +1,109 @@
-using collAnon.Client.Services;
+using collAnon.Client.Services;
+
+using decePubClient.Services;
+
 using Microsoft.AspNetCore.Components;
 
 namespace decePubClient.LayerComponents
 {
-	public class LocalizableComponentBase : ComponentBase
+	/// <summary>
+	/// Base of every page and app component (b2b.next's WidmannComponentBase). It gives them the cascading state, the
+	/// localizer, navigation and toasts, the loading flag and the disable rule, and the offline helpers: a page that
+	/// finds the app offline registers its fetch with WhenOnline, starts StartOnlinePolling and stops loading; the
+	/// job runs once when the app is back online.
+	/// </summary>
+	public class LocalizableComponentBase : ComponentBase, IAsyncDisposable
 	{
+		[CascadingParameter] protected CascadingState CascadingState { get; set; }
 		[Inject] public CoalescingStringLocalizer Localizer { get; set; }
-		protected List<Func<Task>> AfterRenderAsyncJobs = new();
+		[Inject] protected NavigationManager Navigation { get; set; }
+		[Inject] protected ToastService Toast { get; set; }
+
+		/// <summary>Work to run once after the next render, e.g. JS interop that needs the rendered DOM.</summary>
+		protected List<Func<Task>> AfterRenderAsyncJobs = [];
+
+		/// <summary>True until the component's first load completes; set it to false at the end of OnInitializedAsync.</summary>
 		protected bool IsLoading { get; set; } = true;
+
+		/// <summary>What every Disabled= binding starts from: loading, or no connection.</summary>
+		protected bool IsDefaultDisabled => IsLoading || CascadingState.IsOffline;
+
+		readonly List<Func<Task>> onOnlineJobs = [];
+		PeriodicTimer pollingTimer;
+		CancellationTokenSource pollingCancellation;
+		bool disposed;
+
+		protected override async Task OnAfterRenderAsync(bool firstRender)
+		{
+			if (AfterRenderAsyncJobs.Count == 0)
+				return;
+
+			var jobs = AfterRenderAsyncJobs.ToList();
+			AfterRenderAsyncJobs.Clear();
+			foreach (var job in jobs)
+				await job();
+		}
+
+		/// <summary>Runs the job once, the next time the app is online (needs StartOnlinePolling).</summary>
+		protected void WhenOnline(Func<Task> job) => onOnlineJobs.Add(job);
+
+		/// <summary>Checks every interval (10 seconds by default) whether the app is back online to run the WhenOnline jobs.</summary>
+		protected void StartOnlinePolling(TimeSpan? interval = null)
+		{
+			if (pollingTimer is not null)
+				return;
+
+			pollingCancellation = new();
+			pollingTimer = new(interval ?? TimeSpan.FromSeconds(10));
+			_ = PollOnline(pollingCancellation.Token);
+		}
+
+		async Task PollOnline(CancellationToken cancellationToken)
+		{
+			try
+			{
+				while (await pollingTimer.WaitForNextTickAsync(cancellationToken))
+				{
+					if (CascadingState.IsOffline || onOnlineJobs.Count == 0)
+						continue;
+
+					var jobs = onOnlineJobs.ToList();
+					onOnlineJobs.Clear();
+					foreach (var job in jobs)
+					{
+						try
+						{
+							await InvokeAsync(job);
+						}
+						catch (Exception ex)
+						{
+							await CascadingState.ProcessError(ex, $"{GetType().Name}.{nameof(PollOnline)}", cancellationToken);
+						}
+					}
+
+					await InvokeAsync(StateHasChanged);
+				}
+			}
+			catch (OperationCanceledException)
+			{
+			}
+		}
+
+		public virtual async ValueTask DisposeAsync()
+		{
+			if (disposed)
+				return;
+
+			disposed = true;
+			if (pollingCancellation is not null)
+			{
+				await pollingCancellation.CancelAsync();
+				pollingCancellation.Dispose();
+			}
+
+			pollingTimer?.Dispose();
+			onOnlineJobs.Clear();
+			GC.SuppressFinalize(this);
+		}
 	}
 }