feat: 添加客服在线状态和聊天粘贴图片功能

**客服在线状态：**
- 后端：添加 admin_users.support_status 字段（online/offline/busy）
- 接口：PUT /admin/me/support-status 更新状态
- 前端：管理员顶部导航显示状态切换器（仅客服权限可见）
- 转接对话框显示客服在线状态和智能排序（在线优先）

**聊天粘贴图片：**
- 用户端、移动端、管理端聊天输入框支持 Ctrl+V/Cmd+V 直接粘贴图片
- 自动调用图片压缩和上传逻辑，与文件选择上传保持一致
- 最多支持粘贴9张图片

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/internal/modules/adminauth/dto.go

@@ -7,13 +7,14 @@ import (
 )
 
 type AdminDTO struct {
-	ID          uint64     `json:"id"`
-	Username    string     `json:"username"`
-	Nickname    string     `json:"nickname"`
-	Status      string     `json:"status"`
-	Roles       []RoleDTO  `json:"roles"`
-	Permissions []string   `json:"permissions"`
-	LastLoginAt *time.Time `json:"last_login_at"`
+	ID            uint64     `json:"id"`
+	Username      string     `json:"username"`
+	Nickname      string     `json:"nickname"`
+	Status        string     `json:"status"`
+	SupportStatus string     `json:"support_status"`
+	Roles         []RoleDTO  `json:"roles"`
+	Permissions   []string   `json:"permissions"`
+	LastLoginAt   *time.Time `json:"last_login_at"`
 }
 
 type RoleDTO struct {
@@ -39,3 +40,7 @@ type CaptchaDTO struct {
 	Image     string `json:"image"`
 	ExpiresIn int64  `json:"expires_in"`
 }
+
+type UpdateSupportStatusRequest struct {
+	Status string `json:"status" binding:"required,oneof=online offline busy"`
+}

backend/internal/modules/adminauth/handler.go

@@ -65,6 +65,33 @@ func (h *Handler) Logout(c *gin.Context) {
 	response.OK(c, gin.H{"logged_out": true})
 }
 
+func (h *Handler) UpdateSupportStatus(c *gin.Context) {
+	adminID, ok := currentAdminID(c)
+	if !ok {
+		response.Unauthorized(c, "缺少管理员上下文")
+		return
+	}
+	var req UpdateSupportStatusRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, "状态值无效，必须是 online、offline 或 busy")
+		return
+	}
+	if err := h.service.UpdateSupportStatus(adminID, req.Status); err != nil {
+		writeAdminAuthError(c, err)
+		return
+	}
+	response.OK(c, gin.H{"updated": true, "support_status": req.Status})
+}
+
+func currentAdminID(c *gin.Context) (uint64, bool) {
+	value, ok := c.Get(middleware.ContextAdminID)
+	if !ok {
+		return 0, false
+	}
+	adminID, ok := value.(uint64)
+	return adminID, ok
+}
+
 type AdminRefreshRequest struct {
 	RefreshToken string `json:"refresh_token" binding:"required"`
 }

backend/internal/modules/adminauth/repository.go

@@ -126,6 +126,18 @@ func (r *Repository) FindByID(id uint64) (*AdminDTO, error) {
 	return &dto, nil
 }
 
+func (r *Repository) UpdateSupportStatus(adminID uint64, status string) error {
+	if r.db == nil {
+		return ErrDependencyUnavailable
+	}
+	if status != "online" && status != "offline" && status != "busy" {
+		return errors.New("invalid support status")
+	}
+	return r.db.Model(&model.AdminUser{}).
+		Where("id = ?", adminID).
+		Update("support_status", status).Error
+}
+
 func (r *Repository) ensureDefaultAdmin() error {
 	var count int64
 	if err := r.db.Model(&model.AdminUser{}).Count(&count).Error; err != nil {
@@ -162,11 +174,12 @@ func (r *Repository) ensureDefaultAdmin() error {
 
 func toDTO(admin model.AdminUser) AdminDTO {
 	return AdminDTO{
-		ID:          admin.ID,
-		Username:    admin.Username,
-		Nickname:    admin.Nickname,
-		Status:      admin.Status,
-		LastLoginAt: admin.LastLoginAt,
+		ID:            admin.ID,
+		Username:      admin.Username,
+		Nickname:      admin.Nickname,
+		Status:        admin.Status,
+		SupportStatus: admin.SupportStatus,
+		LastLoginAt:   admin.LastLoginAt,
 	}
 }
 

backend/internal/modules/adminauth/service.go

@@ -61,3 +61,10 @@ func (s *Service) Me(adminID uint64) (*AdminDTO, error) {
 	}
 	return s.repo.FindByID(adminID)
 }
+
+func (s *Service) UpdateSupportStatus(adminID uint64, status string) error {
+	if s.repo == nil {
+		return ErrDependencyUnavailable
+	}
+	return s.repo.UpdateSupportStatus(adminID, status)
+}