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_tabs/lib/main.dart

@@ -12,6 +12,8 @@ void main() {
 }
 
 class MyHome extends StatefulWidget {
+  const MyHome({super.key});
+
   @override
   MyHomeState createState() => MyHomeState();
 }

using_tabs/lib/tabs/first.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/material.dart';
 
 class First extends StatelessWidget {
+  const First({super.key});
+
   @override
   Widget build(BuildContext context) {
     return Container(

using_tabs/lib/tabs/second.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/material.dart';
 
 class Second extends StatelessWidget {
+  const Second({super.key});
+
   @override
   Widget build(BuildContext context) {
     return Container(

using_tabs/lib/tabs/third.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/material.dart';
 
 class Third extends StatelessWidget {
+  const Third({super.key});
+
   @override
   Widget build(BuildContext context) {
     return Container(