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

android/app/capacitor.build.gradle

@@ -12,6 +12,7 @@ dependencies {
     implementation project(':capacitor-app')
     implementation project(':capacitor-camera')
     implementation project(':capacitor-filesystem')
+    implementation project(':capacitor-share')
     implementation project(':capawesome-capacitor-file-picker')
 
 }