feat: spin-mobile — Flutter WebView 셸 (Android·iOS)

prod 웹앱(spin.special-partners.com)을 감싸는 네이티브 셸. 화면 개발 없음.
- InAppWebView: 쿠키/캐시 영속·UA(spinApp) 태그·풀투리프레시·외부링크 분기·오프라인 화면
- Android 하드웨어 뒤로가기(웹 히스토리→더블탭 종료), navy 스플래시/상태바
- 파일/카메라 업로드 권한(Android/iOS), 생체인증 잠금(local_auth)
- FCM 푸시(firebase_messaging) — 설정 전 자동 비활성, 토큰은 웹 세션으로 /api/devices 등록
- prod URL 고정(app_config.dart)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ios/Runner/Assets.xcassets/LaunchImage.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "filename" : "LaunchImage.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "LaunchImage@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "LaunchImage@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

ios/Runner/Assets.xcassets/LaunchImage.imageset/README.md

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+# Launch Screen Assets
+
+You can customize the launch screen with your own desired assets by replacing the image files in this directory.
+
+You can also do it by opening your Flutter project's Xcode project with `open ios/Runner.xcworkspace`, selecting `Runner/Assets.xcassets` in the Project Navigator and dropping in the desired images.