test: add comprehensive test coverage and improve code quality

- Add new test files for auth, service, and handler modules
- Improve test organization and coverage
- Refactor code for better maintainability
- Add captcha, settings, stats, and theme handler tests
- Add auth module tests (CAS, OAuth, password, SSO, state)
- Add service layer tests for auth, export, permissions, roles
- All Go tests pass (exit code 0)
- All frontend tests pass (325 tests in 59 files)

internal/monitoring/slo.go

@@ -10,7 +10,7 @@ import (
 // 这些指标是 SLO 测量的基础，用于计算错误预算燃烧率
 type SLOMetrics struct {
 	// 缓存命中统计（alerts.yml 引用但原来未定义）
-	CacheHitsTotal      *prometheus.CounterVec
+	CacheHitsTotal       *prometheus.CounterVec
 	CacheOperationsTotal *prometheus.CounterVec
 
 	// 数据库连接池状态（alerts.yml 引用但原来未定义）
@@ -21,8 +21,8 @@ type SLOMetrics struct {
 	TokenRefreshTotal *prometheus.CounterVec
 
 	// 账号安全事件
-	AccountLockTotal      prometheus.Counter
-	AnomalyDetectedTotal  *prometheus.CounterVec
+	AccountLockTotal     prometheus.Counter
+	AnomalyDetectedTotal *prometheus.CounterVec
 
 	// 错误预算燃烧率（可选，用于自定义仪表盘）
 	ErrorBudgetBurnRate *prometheus.GaugeVec