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_stepper/lib/main.dart

@@ -9,6 +9,8 @@ void main() {
 }
 
 class MyHome extends StatefulWidget {
+  const MyHome({super.key});
+
   @override
   MyHomeState createState() => MyHomeState();
 }
@@ -47,7 +49,7 @@ class MyHomeState extends State<MyHome> {
       body: Container(
           child: Stepper(
         // Using a variable here for handling the currentStep
-        currentStep: this.current_step,
+        currentStep: current_step,
         // List the steps you would like to have
         steps: my_steps,
         // Define the type of Stepper style
@@ -63,7 +65,7 @@ class MyHomeState extends State<MyHome> {
             current_step = step;
           });
           // Log function call
-          print("onStepTapped : " + step.toString());
+          print("onStepTapped : $step");
         },
         onStepCancel: () {
           // On hitting cancel button, change the state
@@ -77,7 +79,7 @@ class MyHomeState extends State<MyHome> {
             }
           });
           // Log function call
-          print("onStepCancel : " + current_step.toString());
+          print("onStepCancel : $current_step");
         },
         // On hitting continue button, change the state
         onStepContinue: () {
@@ -91,7 +93,7 @@ class MyHomeState extends State<MyHome> {
             }
           });
           // Log function call
-          print("onStepContinue : " + current_step.toString());
+          print("onStepContinue : $current_step");
         },
       )),
     );