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

using_edittext/lib/main.dart

@@ -7,6 +7,8 @@ void main() {
 }
 
 class MyEditText extends StatefulWidget {
+  const MyEditText({super.key});
+
   @override
   MyEditTextState createState() => MyEditTextState();
 }
@@ -33,7 +35,7 @@ class MyEditTextState extends State<MyEditText> {
                 decoration: InputDecoration(hintText: "Enter text here..."),
                 onSubmitted: (String str) {
                   setState(() {
-                    results = results + "\n" + str;
+                    results = "$results\n$str";
                     controller.text = "";
                   });
                 },