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/Plugin.cs

@@ -307,11 +307,13 @@ public sealed class Plugin : IAsyncDalamudPlugin
             cancellationToken.ThrowIfCancellationRequested();
 
             // Container drives service init now: Host.StartAsync triggers the
-            // IHostedService adapters (FontManager.BuildFonts, ThemeRegistry
-            // cache warmup + Switch, IPC eager-resolve, MessageManager
-            // FilterAllTabsAsync, AutoTellTabsService.Initialize). Window
-            // registration with WindowSystem runs on the framework thread
-            // inside PluginLifecycle.LoadAsync after StartAsync returns.
+            // remaining IHostedService adapters (ThemeRegistry cache warmup +
+            // Switch, IPC eager-resolve, MessageManager FilterAllTabsAsync,
+            // AutoTellTabsService.Initialize). FontManager runs its own init
+            // inline inside the ctor's SuppressAutoRebuild block on eager
+            // resolve. Window registration with WindowSystem runs on the
+            // framework thread inside PluginLifecycle.LoadAsync after
+            // StartAsync returns.
             if (_lifecycle is not null)
                 await _lifecycle.LoadAsync(cancellationToken).ConfigureAwait(false);
 
@@ -911,7 +913,10 @@ public sealed class Plugin : IAsyncDalamudPlugin
         Interface.UiBuilder.DisableUserUiHide = !Config.HideWhenUiHidden;
         ChatLogWindow.DefaultText = ImGui.GetStyle().Colors[(int)ImGuiCol.Text];
 
-        using ((Config.FontsEnabled ? FontManager.RegularFont : FontManager.Axis).Push())
+        // RegularFont is nullable only because the live rebuild path
+        // disposes it before reassigning; both ends of that swap happen on
+        // this same draw thread, so it cannot be null here.
+        using ((Config.FontsEnabled ? FontManager.RegularFont! : FontManager.Axis).Push())
             WindowSystem.Draw();
 
         ChatLogWindow.FinalizeFrame();