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

covid19_mobile_app/lib/screens/countrylist.dart

@@ -8,6 +8,8 @@ import 'dart:convert';
 import 'package:folding_cell/folding_cell.dart';
 
 class CountryList extends StatelessWidget {
+  const CountryList({super.key});
+
   @override
   Widget build(BuildContext context) {
     List<dynamic> results = [];
@@ -31,25 +33,27 @@ class CountryList extends StatelessWidget {
       body: FutureBuilder(
         future: getAllCountriesData(),
         builder: (context, snapshot) {
-          if (snapshot.connectionState == ConnectionState.waiting)
+          if (snapshot.connectionState == ConnectionState.waiting) {
             return Center(
               child: CircularProgressIndicator(),
             );
-          if (snapshot.hasError)
+          }
+          if (snapshot.hasError) {
             return Center(
               child: Text("Error! please check you wifi connection"),
             );
+          }
           results = jsonDecode(snapshot.data);
           return ListView.builder(
             physics: BouncingScrollPhysics(),
             itemCount: results.length,
             itemBuilder: (context, index) {
-              var _foldingCellKey = GlobalKey<SimpleFoldingCellState>();
+              var foldingCellKey = GlobalKey<SimpleFoldingCellState>();
               return Container(
                 color: Color(0xFF2e282a),
                 alignment: Alignment.topCenter,
                 child: SimpleFoldingCell.create(
-                  key: _foldingCellKey,
+                  key: foldingCellKey,
                   frontWidget: Builder(
                     builder: (BuildContext context) {
                       return GestureDetector(