feat(themes): apply theme typography font-size overrides on every activation path

HellionChat/Infrastructure/Hosting/InitHostedServices.cs

@@ -16,16 +16,26 @@ namespace HellionChat.Infrastructure.Hosting;
 // at Build, which runs the service ctor (IPC subscribe etc.) right then
 // instead of lazily on first GetRequiredService.
 
-internal sealed class ThemeRegistryInitHostedService(ThemeRegistry registry) : IHostedService
+internal sealed class ThemeRegistryInitHostedService(
+    ThemeRegistry registry,
+    FontManager fontManager
+) : IHostedService
 {
-    public Task StartAsync(CancellationToken cancellationToken)
+    public async Task StartAsync(CancellationToken cancellationToken)
     {
         // Materialise the lazy AllCustom enumerable so the slug lookup hits a
         // warm cache; otherwise the first Switch falls through to the built-in
         // default when Config.Theme points at a custom slug.
         foreach (var _ in registry.AllCustom()) { }
         registry.SwitchSilent(Plugin.Config.Theme);
-        return Task.CompletedTask;
+
+        // B4b-3: point font sizes at the active theme's typography, wire future
+        // theme switches to the atlas rebuild, and apply the boot theme's override.
+        fontManager.SetTypographySource(() => registry.Active.Typography);
+        registry.SetActiveChangedCallback(() => fontManager.RebuildDelegateFontsIfChanged());
+        await Plugin.Framework.RunOnFrameworkThread(() =>
+            fontManager.RebuildDelegateFontsIfChanged()
+        );
     }
 
     public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;