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/database/db.go

@@ -70,7 +70,6 @@ func NewDB(cfg *config.Config) (*DB, error) {
 	return &DB{DB: db}, nil
 }
 
-
 func (db *DB) AutoMigrate(cfg *config.Config) error {
 	log.Println("starting database migration")
 	if err := db.DB.AutoMigrate(