feat(rpm): RPM 限流模块优化

P0:
- rpm_override 嵌入 Auth Cache Snapshot，消除每请求 DB 查询 (snapshot v6→v7)
- 429 RPM 响应返回 Retry-After 头（当前分钟剩余秒数）

P1:
- ClearAll 按钮直连 DELETE API，带 loading 防重复
- 新增 GET /admin/users/:id/rpm-status 管理员 RPM 用量查询端点

优化:
- checkRPM 从级联互斥改为并行取最严，user.rpm_limit 作为全局硬上限始终生效
- Override/Group 变更后自动失效 auth cache
- fail-open 语义不变，Redis 故障不阻塞业务

backend/internal/handler/admin/group_handler.go

@@ -110,6 +110,8 @@ type CreateGroupRequest struct {
 	RequirePrivacySet           bool                                      `json:"require_privacy_set"`
 	DefaultMappedModel          string                                    `json:"default_mapped_model"`
 	MessagesDispatchModelConfig service.OpenAIMessagesDispatchModelConfig `json:"messages_dispatch_model_config"`
+	// 分组 RPM 上限（0 = 不限制）
+	RPMLimit int `json:"rpm_limit"`
 	// 从指定分组复制账号（创建后自动绑定）
 	CopyAccountsFromGroupIDs []int64 `json:"copy_accounts_from_group_ids"`
 }
@@ -145,6 +147,8 @@ type UpdateGroupRequest struct {
 	RequirePrivacySet           *bool                                      `json:"require_privacy_set"`
 	DefaultMappedModel          *string                                    `json:"default_mapped_model"`
 	MessagesDispatchModelConfig *service.OpenAIMessagesDispatchModelConfig `json:"messages_dispatch_model_config"`
+	// 分组 RPM 上限（0 = 不限制）；nil 表示未提供不改动
+	RPMLimit *int `json:"rpm_limit"`
 	// 从指定分组复制账号（同步操作：先清空当前分组的账号绑定，再绑定源分组的账号）
 	CopyAccountsFromGroupIDs []int64 `json:"copy_accounts_from_group_ids"`
 }
@@ -262,6 +266,7 @@ func (h *GroupHandler) Create(c *gin.Context) {
 		RequirePrivacySet:               req.RequirePrivacySet,
 		DefaultMappedModel:              req.DefaultMappedModel,
 		MessagesDispatchModelConfig:     req.MessagesDispatchModelConfig,
+		RPMLimit:                        req.RPMLimit,
 		CopyAccountsFromGroupIDs:        req.CopyAccountsFromGroupIDs,
 	})
 	if err != nil {
@@ -313,6 +318,7 @@ func (h *GroupHandler) Update(c *gin.Context) {
 		RequirePrivacySet:               req.RequirePrivacySet,
 		DefaultMappedModel:              req.DefaultMappedModel,
 		MessagesDispatchModelConfig:     req.MessagesDispatchModelConfig,
+		RPMLimit:                        req.RPMLimit,
 		CopyAccountsFromGroupIDs:        req.CopyAccountsFromGroupIDs,
 	})
 	if err != nil {
@@ -477,6 +483,51 @@ func (h *GroupHandler) BatchSetGroupRateMultipliers(c *gin.Context) {
 	response.Success(c, gin.H{"message": "Rate multipliers updated successfully"})
 }
 
+// BatchSetGroupRPMOverridesRequest represents batch set rpm_override request
+type BatchSetGroupRPMOverridesRequest struct {
+	Entries []service.GroupRPMOverrideInput `json:"entries" binding:"required"`
+}
+
+// BatchSetGroupRPMOverrides handles batch setting rpm_override for users in a group
+// PUT /api/v1/admin/groups/:id/rpm-overrides
+func (h *GroupHandler) BatchSetGroupRPMOverrides(c *gin.Context) {
+	groupID, err := strconv.ParseInt(c.Param("id"), 10, 64)
+	if err != nil {
+		response.BadRequest(c, "Invalid group ID")
+		return
+	}
+
+	var req BatchSetGroupRPMOverridesRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, "Invalid request: "+err.Error())
+		return
+	}
+
+	if err := h.adminService.BatchSetGroupRPMOverrides(c.Request.Context(), groupID, req.Entries); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+
+	response.Success(c, gin.H{"message": "RPM overrides updated successfully"})
+}
+
+// ClearGroupRPMOverrides handles clearing all rpm_override for a group
+// DELETE /api/v1/admin/groups/:id/rpm-overrides
+func (h *GroupHandler) ClearGroupRPMOverrides(c *gin.Context) {
+	groupID, err := strconv.ParseInt(c.Param("id"), 10, 64)
+	if err != nil {
+		response.BadRequest(c, "Invalid group ID")
+		return
+	}
+
+	if err := h.adminService.ClearGroupRPMOverrides(c.Request.Context(), groupID); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+
+	response.Success(c, gin.H{"message": "RPM overrides cleared successfully"})
+}
+
 // UpdateSortOrderRequest represents the request to update group sort orders
 type UpdateSortOrderRequest struct {
 	Updates []struct {