Migrate to Avalonia 12 and Plugin SDK v5

Upgrade project to the Avalonia 12 baseline and Plugin SDK v5: centralize Avalonia packages, remove legacy WebView.Avalonia usage (use NativeWebView/WebView2 EnvironmentRequested), and update Fluent/Material icon/package usages. Bump multiple package/project versions to 5.0.0 and Avalonia 12.0.1, update plugin template and README/docs to SDK v5, and add PLUGIN_SDK_V5_MIGRATION.md.

Also fix runtime/behavior bugs: make DataLocationResolver use a fixed bootstrap launcher data path and avoid recursive ResolveDataRoot; add legacy-state handling and extraction in OobeStateService; and update component settings tests to reflect migrated storage (DB/backup) and reset cache for test reloads. Various csproj, tests, and docs updated to reflect the migration and ensure build/test compatibility.

docs/Plugins develop/07-发布与运营/01-插件打包规范.md

@@ -33,7 +33,7 @@ MyPlugin.laapp
   "description": "插件描述",
   "author": "作者名",
   "version": "1.0.0",
-  "apiVersion": "4.0.1",
+  "apiVersion": "5.0.0",
   "entranceAssembly": "MyPlugin.dll",
   "sharedContracts": []
 }
@@ -61,7 +61,7 @@ MyPlugin.laapp
   </PropertyGroup>
   
   <ItemGroup>
-    <PackageReference Include="LanMountainDesktop.PluginSdk" Version="4.0.1" />
+    <PackageReference Include="LanMountainDesktop.PluginSdk" Version="5.0.0" />
   </ItemGroup>
   
   <!-- 确保资源文件复制到输出目录 -->