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_api_account.go

@@ -0,0 +1,59 @@
+package controller
+
+import (
+	"net/http"
+
+	"metazone.cc/metalab/internal/common"
+
+	"github.com/gin-gonic/gin"
+)
+
+// ChangePassword 修改密码（需登录）
+func (sc *SettingsController) ChangePassword(c *gin.Context) {
+	uid, exists := c.Get("uid")
+	if !exists {
+		common.Error(c, http.StatusUnauthorized, "请先登录")
+		return
+	}
+
+	var req struct {
+		CurrentPassword string `json:"current_password" binding:"required"`
+		NewPassword     string `json:"new_password" binding:"required,min=8"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		common.Error(c, http.StatusBadRequest, "请检查输入")
+		return
+	}
+
+	if err := sc.authService.ChangePassword(uid.(uint), req.CurrentPassword, req.NewPassword); err != nil {
+		handleSettingsError(c, err)
+		return
+	}
+
+	common.OkMessage(c, "密码已修改，请重新登录")
+}
+
+// DeleteAccount 自助注销账号（需登录，验证密码 + 注销原因）
+func (sc *SettingsController) DeleteAccount(c *gin.Context) {
+	uid, exists := c.Get("uid")
+	if !exists {
+		common.Error(c, http.StatusUnauthorized, "请先登录")
+		return
+	}
+
+	var req struct {
+		Password string `json:"password" binding:"required"`
+		Reason   string `json:"reason"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		common.Error(c, http.StatusBadRequest, "请检查输入")
+		return
+	}
+
+	if err := sc.authService.DeleteAccount(uid.(uint), req.Password, req.Reason); err != nil {
+		handleSettingsError(c, err)
+		return
+	}
+
+	common.OkMessage(c, "账号已注销，7 天内重新登录即可恢复")
+}