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/homePage.dart

@@ -207,24 +207,6 @@ class _HomePageState extends State<HomePage> {
         });
   }
 
-  void _showDialog(String message) {
-    final BuildContext? context = _scaffoldKey.currentContext;
-    if (context == null) return;
-    showDialog<bool>(
-        context: context,
-        builder: (_) => AlertDialog(
-              content: Text(message),
-              actions: <Widget>[
-                TextButton(
-                  child: Text(S.of(context).CLOSE),
-                  onPressed: () {
-                    Navigator.pop(context);
-                  },
-                ),
-              ],
-            ));
-  }
-
   void _showItemDialog(Map<String, dynamic> message, FireNotification notif) {
     final BuildContext? context = _scaffoldKey.currentContext;
     if (context == null) return;
@@ -236,7 +218,6 @@ class _HomePageState extends State<HomePage> {
         _navigateToItemDetail(message);
       }
     }).catchError((Object e) {
-      print('$e');
     });
   }