feat: add multi-environment support (development, staging, production)

- Replace dotenv with compile-time dart-define-from-file config per flavor
  - Add Android product flavors with applicationIdSuffix and per-flavor AndroidManifest
  - Add iOS build configurations, schemes, per-flavor plists and entitlements
  - Configure ProGuard rules for R8 compatibility with Entrust/Antelop SDK
  - Restructure assets into shared/ and per-flavor directories
  - Generate per-flavor launcher icons for Android and iOS
  - Refactor app initialization into initApp() with per-flavor entry points
  - Update asset paths across auth, home, profile, splash modules and sf_shared

apps/mobile_app/pubspec.lock

@@ -362,14 +362,6 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
-  flutter_dotenv:
-    dependency: "direct main"
-    description:
-      name: flutter_dotenv
-      sha256: d4130c4a43e0b13fefc593bc3961f2cb46e30cb79e253d4a526b1b5d24ae1ce4
-      url: "https://pub.dev"
-    source: hosted
-    version: "6.0.0"
   flutter_launcher_icons:
     dependency: "direct dev"
     description: