Migrate to Electron and implement native PDF export

Major changes:
- Migrate from Tauri to Electron as primary desktop runtime
- Implement native print dialog for PDF export via Electron webview
- Add desktop runtime abstraction layer (supports both Electron and Tauri)
- Implement task list rendering in preview mode
- Add favorite notes sorting to display starred notes at top
- Add attachment upload functionality with file picker
- Improve sync reliability and Unicode filename support
- Add category color sync across devices via WebDAV
- Update documentation for Electron workflow

Technical improvements:
- Add Electron main process and preload bridge
- Create desktop service layer for runtime-agnostic operations
- Implement runtimeFetch for proxying network requests through Electron
- Add PrintView component for native print rendering
- Extract print/PDF utilities to shared module
- Update build configuration for Electron integration

.gitignore

@@ -10,6 +10,7 @@ lerna-debug.log*
 node_modules
 dist
 dist-ssr
+release
 *.local
 
 # Editor directories and files