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/api/handler/user_handler.go

@@ -515,7 +515,7 @@ func (h *UserHandler) CreateAdmin(c *gin.Context) {
 	var req struct {
 		Username string `json:"username" binding:"required"`
 		Password string `json:"password" binding:"required"`
-		Email   string `json:"email"`
+		Email    string `json:"email"`
 		Nickname string `json:"nickname"`
 	}
 
@@ -527,7 +527,7 @@ func (h *UserHandler) CreateAdmin(c *gin.Context) {
 	adminReq := &service.CreateAdminRequest{
 		Username: req.Username,
 		Password: req.Password,
-		Email:   req.Email,
+		Email:    req.Email,
 		Nickname: req.Nickname,
 	}