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>

src-tauri/tauri.conf.json

@@ -53,43 +53,15 @@
     "macOS": {
       "frameworks": [],
       "minimumSystemVersion": "10.13",
+      "entitlements": null,
       "exceptionDomain": "",
       "signingIdentity": null,
-      "entitlements": null,
-      "providerShortName": null,
-      "dmg": {
-        "contents": [
-          {
-            "x": 130,
-            "y": 220
-          },
-          {
-            "x": 410,
-            "y": 220,
-            "type": "link",
-            "path": "/Applications"
-          }
-        ],
-        "window": {
-          "width": 540,
-          "height": 380
-        }
-      }
+      "providerShortName": null
     },
     "windows": {
       "certificateThumbprint": null,
       "digestAlgorithm": "sha256",
       "timestampUrl": "",
-      "nsis": {
-        "displayLanguageSelector": false,
-        "languages": ["English", "SimpChinese"],
-        "template": false,
-        "installMode": "perMachine",
-        "allowDowngrades": true,
-        "createDesktopShortcut": true,
-        "createStartMenuShortcut": true,
-        "multiUserLauncher": false
-      },
       "wix": {
         "language": ["en-US", "zh-CN"]
       },