fix: improve file sharing on Android using app-private storage

- Replace direct file writing with app-private storage + share dialog
- Add Share plugin for cross-platform file sharing
- Update file paths configuration for Android
- Fix permission issues by using Directory.Data instead of Documents
- Simplify file export flow in DataExportSection

package.json

@@ -50,6 +50,7 @@
     "@capacitor/core": "^6.2.0",
     "@capacitor/filesystem": "^6.0.0",
     "@capacitor/ios": "^6.2.0",
+    "@capacitor/share": "^6.0.3",
     "@capawesome/capacitor-file-picker": "^6.2.0",
     "@dicebear/collection": "^5.4.1",
     "@dicebear/core": "^5.4.1",