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

image_editor/lib/SaveInGallery.dart

@@ -2,10 +2,9 @@ import 'package:flutter/material.dart';
 import 'package:gallery_saver_plus/gallery_saver.dart';
 import 'package:fluttertoast/fluttertoast.dart';
 
-SaveImg(_image) async {
-  var result =
-      await GallerySaver.saveImage(_image.path, albumName: 'ImageEditor')
-          .then((bool? success) {
+Future<void> SaveImg(image) async {
+  await GallerySaver.saveImage(image.path, albumName: 'ImageEditor')
+      .then((bool? success) {
     success == true
         ? Fluttertoast.showToast(
             msg: "Image saved in gallery/ImageEditor",