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.

NuGet.Config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <config>
+    <!-- 相对本文件：包落在仓库目录下，与仓库同盘（本机 D:），避免依赖 C:\Temp\cursor-sandbox-cache 等易损路径 -->
+    <add key="globalPackagesFolder" value=".nuget/packages" />
+  </config>
+</configuration>