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/testdb/testdb.go

@@ -5,10 +5,10 @@ package testdb
 import (
 	"testing"
 
-	_ "modernc.org/sqlite" // 注册纯Go SQLite驱动，驱动名 "sqlite"
 	gormsqlite "gorm.io/driver/sqlite"
 	"gorm.io/gorm"
 	"gorm.io/gorm/logger"
+	_ "modernc.org/sqlite" // 注册纯Go SQLite驱动，驱动名 "sqlite"
 )
 
 // Open 使用 modernc.org/sqlite（纯Go，无需CGO）打开内存测试数据库。