fix: address code review issues for RPM limiting feature

- Use TxPipeline (MULTI/EXEC) instead of Pipeline for atomic INCR+EXPIRE
- Filter negative values in GetBaseRPM(), update test expectation
- Add RPM batch query (GetRPMBatch) to account List API
- Add warn logs for RPM increment failures in gateway handler
- Reset enableRpmLimit on BulkEditAccountModal close
- Use union type 'tiered' | 'sticky_exempt' for rpmStrategy refs
- Add design decision comments for rdb.Time() RTT trade-off

backend/internal/handler/gateway_handler.go

@@ -368,8 +368,8 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 
 			// RPM 计数递增（调度成功后、Forward 前）
 			if account.IsAnthropicOAuthOrSetupToken() && account.GetBaseRPM() > 0 {
-				if h.gatewayService.IncrementAccountRPM(c.Request.Context(), account.ID) != nil {
-					// 失败开放：不阻塞请求
+				if err := h.gatewayService.IncrementAccountRPM(c.Request.Context(), account.ID); err != nil {
+					reqLog.Warn("gateway.rpm_increment_failed", zap.Int64("account_id", account.ID), zap.Error(err))
 				}
 			}
 
@@ -558,8 +558,8 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 
 			// RPM 计数递增（调度成功后、Forward 前）
 			if account.IsAnthropicOAuthOrSetupToken() && account.GetBaseRPM() > 0 {
-				if h.gatewayService.IncrementAccountRPM(c.Request.Context(), account.ID) != nil {
-					// 失败开放：不阻塞请求
+				if err := h.gatewayService.IncrementAccountRPM(c.Request.Context(), account.ID); err != nil {
+					reqLog.Warn("gateway.rpm_increment_failed", zap.Int64("account_id", account.ID), zap.Error(err))
 				}
 			}