refactor: 拆分超标控制器文件至行数≤120行

- auth_controller.go(238→54): 拆出auth_api_login.go(107)+auth_api_register.go(96)
- settings_controller.go(289→101): 拆出settings_api_profile(116)+account(59)+error_handlers(41)
- message_controller.go(129→85): 拆出message_page_controller.go(55)
- 所有拆分后文件均≤120行，符合code-style.md瘦控制器规范

internal/controller/settings_error_handlers.go

@@ -0,0 +1,41 @@
+package controller
+
+import (
+	"net/http"
+
+	"metazone.cc/metalab/internal/common"
+
+	"github.com/gin-gonic/gin"
+)
+
+// handleSettingsError 统一处理 settings 接口的 service 层错误
+func handleSettingsError(c *gin.Context, err error) {
+	switch err {
+	case common.ErrUsernameTaken:
+		common.Error(c, http.StatusConflict, err.Error())
+	case common.ErrUsernameInvalid:
+		common.Error(c, http.StatusBadRequest, err.Error())
+	case common.ErrBioTooLong:
+		common.Error(c, http.StatusBadRequest, err.Error())
+	case common.ErrIncorrectPassword:
+		common.Error(c, http.StatusForbidden, err.Error())
+	case common.ErrOwnerCannotDelete:
+		common.Error(c, http.StatusForbidden, err.Error())
+	default:
+		common.Error(c, http.StatusInternalServerError, "操作失败")
+	}
+}
+
+// handleAuditSubmitError 统一处理审核提交的错误
+func handleAuditSubmitError(c *gin.Context, err error) {
+	switch err {
+	case common.ErrAuditDisabled:
+		common.Error(c, http.StatusForbidden, "审核功能未开启")
+	case common.ErrAuditTypeOff:
+		common.Error(c, http.StatusForbidden, "该类型审核未开启，请联系管理员")
+	case common.ErrUsernameTaken:
+		common.Error(c, http.StatusConflict, err.Error())
+	default:
+		common.Error(c, http.StatusInternalServerError, "提交审核失败")
+	}
+}