test: Phase 0 测试基础设施 — TestApp + MSW + 覆盖率工具 + CI

- TestApp struct 封装 TestDb + HealthState + tenant_id/operator_id
- TestFixture 工厂方法: create_patient/create_doctor/create_schedule/create_appointment
- 前端 MSW v2 handlers (auth) + server setup + vitest 集成
- vitest coverage v8 配置 + test:coverage script
- GitHub Actions CI: backend (check + test + clippy) + frontend (tsc + test + build)

apps/web/vitest.config.ts

@@ -9,6 +9,12 @@ export default defineConfig({
     globals: true,
     setupFiles: ['./src/test/setup.ts'],
     exclude: ['e2e/**', 'node_modules/**'],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'lcov'],
+      include: ['src/**/*.{ts,tsx}'],
+      exclude: ['src/test/**', 'src/**/*.test.*', 'src/**/*.d.ts'],
+    },
   },
   resolve: {
     alias: {