refactor: standardize Dart and Android config across all 54 apps

- Bump all apps to sdk >=3.0.0 <4.0.0 and add flutter_lints + a shared
  analysis_options.yaml to every app (flutter analyze is now green repo-wide)
- Fix real compile errors in firebase_google_authentication and image_editor,
  plus deprecated APIs (Matrix4, SvgPicture.color, textScaleFactor),
  missing async 'mounted' guards, and misc lints via dart fix + manual fixes
- Align pubspec 'name' with each folder and Android namespace/applicationId
  with the documented github.nisrulz.* convention
- Convert bmi_calculator from a legacy Flutter module to a standard app
  with a proper android/ scaffold; fix missing android:exported in launcher
  manifests across 22 apps so all Android builds pass
- Untrack generated build files (GeneratedPluginRegistrant,
  .flutter-plugins-dependencies) and ignore them

dropdown_button/lib/main.dart

@@ -3,6 +3,8 @@ import 'package:flutter/material.dart';
 void main() => runApp(MyApp());
 
 class MyApp extends StatefulWidget {
+  const MyApp({super.key});
+
   @override
   State<StatefulWidget> createState() {
     return MyAppState();
@@ -10,7 +12,7 @@ class MyApp extends StatefulWidget {
 }
 
 class MyAppState extends State<MyApp> {
-  List<String> _fruits = ["Apple", "Banana", "Pineapple", "Mango", "Grapes"];
+  final List<String> _fruits = ["Apple", "Banana", "Pineapple", "Mango", "Grapes"];
 
   late List<DropdownMenuItem<String>> _dropDownMenuItems;
   late String _selectedFruit;