Refactor settings window UI and theming

Improve theming and layout for the Settings window and related services.

- MaterialSurfaceService: add special material parameters for SettingsWindowBackground (lower alpha, no blur) and avoid hot-switching real backdrops for non-settings windows.
- GlassEffectService: add AdaptiveSettingsWindowTintBrush + ResolveSettingsWindowTintAlpha to provide optional content tinting tied to system material mode.
- SettingsWindowService: refactor theme application into ApplyThemeVariantAndResources, ensure settings window material is applied at show/activate times, and tidy theme/resource application flow.
- SettingsWindow.axaml / .axaml.cs: restructure title bar (separate Grid.Row=0 border) and FANavigationView host, add pane-footer toggle button for :minimal layout, use dynamic corner radius resource, and update toggle/visibility/icon logic and responsive layout code.
- SettingsPages: remove some IconText usages and adjust margins; use DesignCornerRadiusLg for update card corner radius.
- Add NuGet.Config to set local globalPackagesFolder and ignore .nuget/packages in .gitignore.

These changes aim to improve visuals, avoid backdrop overdraw, and make the settings window behavior consistent across themes and layouts.

.gitignore

@@ -6,6 +6,9 @@
 # dotenv files
 .env
 
+# Local NuGet global packages (NuGet.Config globalPackagesFolder)
+.nuget/packages/
+
 # User-specific files
 *.rsuser
 *.suo