fix: migrate to Tauri v2 and fix compilation errors

- Update @tauri-apps/api and @tauri-apps/cli to v2.1.0
- Fix API imports: @tauri-apps/api/core (instead of tauri)
- Add Emitter trait import for event emission
- Export ClassifierConfig from ai module
- Fix private field access: use data_dir() instead of config_dir
- Add serde::Deserialize to AiResult struct
- Fix base64 encoding: use BASE64 Engine API
- Simplify tauri.conf.json for v2 compatibility
- Fix Shortcut::new() call for hotkey module

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

package.json

@@ -16,10 +16,10 @@
     "clean:all": "rm -rf dist node_modules"
   },
   "dependencies": {
-    "@tauri-apps/api": "^1.6.0"
+    "@tauri-apps/api": "^2.1.0"
   },
   "devDependencies": {
-    "@tauri-apps/cli": "^1.6.0",
+    "@tauri-apps/cli": "^2.1.0",
     "terser": "^5.46.0",
     "vite": "^5.4.11"
   }