feat: add deduplicateDownloads setting & fix build errors

- Add deduplicateDownloads field to AppSettings (default: true)
- Add setDeduplicateDownloads() to SettingsNotifier
- Fix type mismatch in files_settings_page (Object → String cast)
- Run build_runner to regenerate settings.g.dart

.github/workflows/release.yml

@@ -76,6 +76,9 @@ jobs:
       - name: Get Flutter dependencies
         run: flutter pub get
 
+      - name: Generate code
+        run: dart run build_runner build --delete-conflicting-outputs
+
       - name: Build APK (Only arm64)
         run: flutter build apk --release --target-platform android-arm64