refactor: clean up 55 lint warnings and issues

- Remove all 31 avoid_print debug statements across codebase
- Fix 8 critical warnings (unused variables, unreachable defaults, etc)
- Update deprecated APIs: launch() → launchUrl(), textScaleFactor → textScaler
- Replace deprecated surfaceVariant → surfaceContainerHighest in Material 3 themes
- Refactor switch statements to use modern pattern matching
- Remove unused code: _showDialog, _initNoLocation, _getAnchorOffset
- Fix use_build_context_synchronously by adding mounted checks
- Add ignore_for_file annotations to generated JSON serialization files
- Fix type annotations in appState.dart and models

Warnings reduced from 301 to 246 issues (8 → 0 critical warnings).
Build verified: app-production-debug.apk (160MB) compiles successfully.
Zero type errors, Dart analysis clean for critical issues.

lib/fileUtils.dart

@@ -35,13 +35,10 @@ Future<String> getFileNameOfLang(
 
 // https://github.com/flutter/flutter/issues/15325
 Future<bool> assetNotExists(String asset) {
-  print('Does not exists $asset ?');
   return rootBundle
       .load(asset)
       .then((_) => false)
       .catchError((Object err, StackTrace stack) {
-    print(err);
-    print(stack);
     return true;
   });
 }