feat(app): 初始化 Flutter 前端项目 (Phase F0)

- Flutter 3.44.0 + Dart 3.12.0
- 设计系统: 7色Token×浅/深模式, NotoSansSC/Caveat字体, 圆角10/16/22/28/pill, 三级阴影
- ResponsiveScaffold: 手机底部TabBar / 平板侧边Rail / 桌面三栏
- go_router 路由表: 13个页面 (5个Tab + 8个全屏页面)
- 13个功能模块占位页面 (home/calendar/mood/search/profile/editor/auth/class/teacher/parent/achievement/stickers/templates)
- 依赖: flutter_bloc, go_router, freezed, isar, dio, perfect_freehand, fl_chart
- 中国镜像: PUB_HOSTED_URL + FLUTTER_STORAGE_BASE_URL
- flutter analyze: No issues found

app/pubspec.yaml

@@ -0,0 +1,79 @@
+name: nuanji_app
+description: "暖记 — 温暖治愈风格的手账日记 App"
+publish_to: 'none'
+version: 0.1.0+1
+
+environment:
+  sdk: ^3.12.0
+
+dependencies:
+  flutter:
+    sdk: flutter
+
+  # 状态管理
+  flutter_bloc: ^9.1.0
+
+  # 路由
+  go_router: ^14.8.0
+
+  # 不可变数据模型
+  freezed_annotation: ^2.4.0
+  json_annotation: ^4.9.0
+
+  # 本地数据库
+  isar: ^3.1.0
+  isar_flutter_libs: ^3.1.0
+
+  # 网络请求
+  dio: ^5.8.0
+
+  # 连接检测
+  connectivity_plus: ^6.1.0
+
+  # 手写引擎
+  perfect_freehand: ^1.0.0
+
+  # 图表
+  fl_chart: ^0.70.0
+
+  # 图片压缩
+  flutter_image_compress: ^2.4.0
+
+  # 工具
+  logger: ^2.5.0
+  uuid: ^4.5.0
+  intl: ^0.19.0
+  path_provider: ^2.1.0
+  share_plus: ^10.1.0
+  permission_handler: ^11.4.0
+
+  # UI 组件
+  cupertino_icons: ^1.0.8
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+
+  # 代码生成
+  build_runner: ^2.4.0
+  freezed: ^2.5.0
+  json_serializable: ^6.8.0
+  isar_generator: ^3.1.0
+
+  # 代码规范
+  flutter_lints: ^6.0.0
+
+flutter:
+  uses-material-design: true
+
+  fonts:
+    - family: NotoSansSC
+      fonts:
+        - asset: assets/fonts/NotoSansSC-Regular.ttf
+        - asset: assets/fonts/NotoSansSC-Bold.ttf
+          weight: 700
+    - family: Caveat
+      fonts:
+        - asset: assets/fonts/Caveat-Regular.ttf
+        - asset: assets/fonts/Caveat-Bold.ttf
+          weight: 700