Avalonia12 (#7)

* ava12升级

* Enable centralized package versioning

Add <Project> and <PropertyGroup> with <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally> to Directory.Packages.props to enable centralized package version management across the repository. This allows package versions to be controlled from this single file instead of individual project files.

* Migrate codebase to Avalonia 12 APIs

Apply Avalonia 12 migration changes: replace SystemDecorations with WindowDecorations and remove ExtendClientAreaChromeHints/ExtendClientAreaTitleBarHeightHint usages; update BindingPlugins removal logic (no-op); switch clipboard usage to ClipboardExtensions.SetTextAsync; update Bitmap.CopyPixels calls to the new signature. Replace TextBox.Watermark with PlaceholderText, convert NumberBox styles to FANumberBox and adjust templates, change Checked/Unchecked handlers to IsCheckedChanged, and adapt FluentIcons usages (SymbolIconSource -> FASymbol/FAFont/FluentIcon equivalents). Fix MainWindow partial classes to inherit Window and correct missing variables/fields/usings. Add migration docs/specs/tasks under .trae and include a small TestFluentIcons project for icon testing.

* 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.

* Update icon glyphs and symbol mappings

Replace and refine icon sources across settings pages and controls: many FAFontIconSource glyphs were updated to specific Seagull Fluent Icons codepoints, some FASymbolIconSource usages were replaced with FAFontIconSource, and a number of symbol-to-Symbol enum mappings were adjusted (e.g. "Bell" -> AlertOn, "Shield" -> ShieldLock). Also clarified a comment in SettingsWindow and fixed a trailing newline in StudySettingsPage. Changes standardize icon visuals and bridge FluentIcons glyphs into FluentAvalonia icon sources.

* fix.修复合并产生的问题。

docs/PRODUCT.md

@@ -39,7 +39,7 @@
 ### 当前阶段
 
 - 产品版本：`1.0.0`
-- Plugin SDK API 基线：`4.0.1`
+- Plugin SDK API 基线：`5.0.0`
 - 当前重点：持续完善宿主体验、设置页体验、组件能力与插件生态
 - 近期需求入口：以 `.trae/specs/` 中的 feature spec 为准
 
@@ -59,4 +59,4 @@
 
 LanMountainDesktop is a cross-platform desktop enhancement product built with Avalonia UI and .NET 10. It targets students, office users, and customization-focused users who want a programmable desktop surface for information, tools, and plugin-driven extensions.
 
-This repository is the source of truth for the desktop host, plugin runtime, Plugin SDK, shared contracts, and core appearance/settings infrastructure. The current product version is `1.0.0`, and the active Plugin SDK baseline in this repository is `4.0.1`.
+This repository is the source of truth for the desktop host, plugin runtime, Plugin SDK, shared contracts, and core appearance/settings infrastructure. The current product version is `1.0.0`, and the active Plugin SDK baseline in this repository is `5.0.0`.