chore: 全面规范化代码，遵循 CLAUDE.md 编码规范

- C# 文件命名改为 snake_case（28 个文件重命名）
- C# 类转换为主构造函数（8 个类）
- 空 catch 添加异常类型（2 处）
- 新建 GlobalUsings.cs（Health.Infrastructure、Health.WebApi）
- Flutter 移除 go_router，改用 Riverpod 路由栈
- Flutter 移除 flutter_secure_storage，改用 sqflite 持久化
- 修复 Flutter 构建路径（Flutter SDK 迁至 D 盘）
- 后端端口改为 0.0.0.0:5000，支持局域网访问

health_app/lib/core/navigation_provider.dart

@@ -0,0 +1,56 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+/// 路由信息
+class RouteInfo {
+  final String name;
+  final Map<String, String> params;
+  const RouteInfo(this.name, {this.params = const {}});
+
+  String param(String key) => params[key] ?? '';
+}
+
+/// 路由栈 Notifier
+class RouteStackNotifier extends Notifier<List<RouteInfo>> {
+  @override
+  List<RouteInfo> build() => [const RouteInfo('login')];
+
+  void replace(String name, {Map<String, String> params = const {}}) {
+    state = [RouteInfo(name, params: params)];
+  }
+
+  void push(String name, {Map<String, String> params = const {}}) {
+    state = [...state, RouteInfo(name, params: params)];
+  }
+
+  void pop() {
+    if (state.length > 1) {
+      state = state.sublist(0, state.length - 1);
+    }
+  }
+}
+
+/// 路由栈 Provider
+final routeStackProvider =
+    NotifierProvider<RouteStackNotifier, List<RouteInfo>>(RouteStackNotifier.new);
+
+/// 当前路由
+final currentRouteProvider = Provider<RouteInfo>((ref) {
+  final stack = ref.watch(routeStackProvider);
+  return stack.last;
+});
+
+/// 跳转（替换整个栈）
+void goRoute(WidgetRef ref, String name, {Map<String, String> params = const {}}) {
+  ref.read(routeStackProvider.notifier).replace(name, params: params);
+}
+
+/// 推入新页面
+void pushRoute(WidgetRef ref, String name, {Map<String, String> params = const {}}) {
+  ref.read(routeStackProvider.notifier).push(name, params: params);
+}
+
+/// 返回上一页
+void popRoute(WidgetRef ref) {
+  ref.read(routeStackProvider.notifier).pop();
+}