chore: 初始化脚手架 — sunny_mochi 企业级 Flutter 模板

Core 基础设施：Flavor 三包体系、Drift+SQLCipher 加密数据库
7 拦截器 Dio 网络栈、CrashReporter 崩溃日志、Sealed Failure 错误体系
5 色板主题系统、Auth 认证骨架（Clean Architecture）、Dev Panel、Mock Adapter

通过验证：flutter analyze（0 errors）、flutter test（全绿）、staging APK 74.8MB

lib/app.dart

@@ -0,0 +1,28 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:sunny_mochi/core/crash/crash_gate.dart';
+import 'package:sunny_mochi/core/router/app_router.dart';
+import 'package:sunny_mochi/core/theme/app_theme.dart';
+import 'package:sunny_mochi/core/theme/theme_notifier.dart';
+
+class App extends ConsumerWidget {
+  const App({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final router = ref.watch(appRouterProvider);
+    final themeMode = ref.watch(themeModeProvider);
+    final scheme = ref.watch(themeProvider);
+
+    return MaterialApp.router(
+      title: 'Sunny Mochi', // TODO: 替换为项目应用名
+      debugShowCheckedModeBanner: false,
+      theme: AppTheme.light(scheme: scheme),
+      darkTheme: AppTheme.dark(scheme: scheme),
+      themeMode: themeMode,
+      routerConfig: router,
+      // CrashGate 在 MaterialApp 内部：showDialog 需要 MaterialLocalizations
+      builder: (context, child) => CrashGate(child: child ?? const SizedBox()),
+    );
+  }
+}