refactor(fonts): hybrid FontManager init via SuppressAutoRebuild

Move font handle creation from BuildFonts() into the FontManager ctor
inside a single atlas.SuppressAutoRebuild() block. Axis, AxisItalic and
FontAwesome become init-only IFontHandle properties; RegularFont and
ItalicFont stay mutable so the live font-settings rebuild path keeps
working without a plugin reload.

- BuildFonts() renamed to RebuildDelegateFonts(), scope reduced to the
  delegate fonts only
- BuildFontsAsync() removed; Task.Run had no purpose with ctor-init
- FontManagerInitHostedService deleted; PluginHostFactory drops the
  matching AddHostedService registration
- PluginHostFactory FontManager registration takes IDalamudPluginInterface
  via factory lambda
- Settings save path now calls RebuildDelegateFonts() instead of
  BuildFonts()
- Plugin.Draw push site gets a null-forgiving for the nullable
  RegularFont with a one-line WHY

HellionChat/Infrastructure/Hosting/InitHostedServices.cs

@@ -11,17 +11,6 @@ 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 FontManagerInitHostedService(FontManager fontManager) : IHostedService
-{
-    public Task StartAsync(CancellationToken cancellationToken)
-    {
-        fontManager.BuildFonts();
-        return Task.CompletedTask;
-    }
-
-    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
-}
-
 internal sealed class ThemeRegistryInitHostedService(ThemeRegistry registry) : IHostedService
 {
     public Task StartAsync(CancellationToken cancellationToken)