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/customStepper.dart

@@ -128,7 +128,7 @@ class CustomStepper extends StatefulWidget {
     this.onCustomStepTapped,
     this.onCustomStepContinue,
     this.onCustomStepCancel,
-  })  : assert(0 <= currentCustomStep && currentCustomStep < steps.length);
+  }) : assert(0 <= currentCustomStep && currentCustomStep < steps.length);
 
   /// The steps of the stepper whose titles, subtitles, icons always get shown.
   ///
@@ -322,14 +322,11 @@ class _CustomStepperState extends State<CustomStepper> {
   }
 
   Widget _buildVerticalControls() {
-    Color cancelColor;
+    // final Color cancelColor;
 
     switch (Theme.of(context).brightness) {
       case Brightness.light:
-        cancelColor = Colors.black54;
-        break;
       case Brightness.dark:
-        cancelColor = Colors.white70;
         break;
     }
 
@@ -341,9 +338,7 @@ class _CustomStepperState extends State<CustomStepper> {
       margin: const EdgeInsets.only(top: 16.0),
       child: ConstrainedBox(
         constraints: const BoxConstraints.tightFor(height: 48.0),
-        child: const Row(
-
-        ),
+        child: const Row(),
       ),
     );
   }