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/widgets/foldable_cell_widgets.dart

@@ -129,13 +129,13 @@ Widget buildInnerBottomWidget(String cases) {
                   context.findAncestorStateOfType<SimpleFoldingCellState>();
               foldingCellState?.toggleFold();
             },
-            child: Text(
-              "Close",
-            ),
             style: TextButton.styleFrom(
               foregroundColor: Colors.black,
               shape: StadiumBorder(),
-              overlayColor: Colors.white.withOpacity(0.5),
+              overlayColor: Colors.white.withValues(alpha: 0.5),
+            ),
+            child: Text(
+              "Close",
             ),
           ),
         ],