fix(routing): 避免路由探测耗尽数据库连接

将跨实例探测协调从持有会话级 advisory lock 改为带过期时间的数据库短租约，避免网络探测期间占用关键 PostgreSQL 连接。新增可配置的探测并发上限和真实 PostgreSQL 回归测试，确保租约生效期间连接池仍可全部获取。\n\n验证：go test ./... -count=1；go vet ./...；真实 PostgreSQL 17 集成测试；迁移安全检查。

apps/api/internal/runner/route_prober.go

@@ -27,6 +27,11 @@ func (s *Service) runRouteHealthProber(ctx context.Context) {
 	ticker := time.NewTicker(time.Second)
 	defer ticker.Stop()
 	states := make(map[string]routeProbeState)
+	probeConcurrency := s.cfg.RouteProbeConcurrency
+	if probeConcurrency <= 0 {
+		probeConcurrency = 8
+	}
+	probeSlots := make(chan struct{}, probeConcurrency)
 	for {
 		select {
 		case <-ctx.Done():
@@ -58,19 +63,35 @@ func (s *Service) runRouteHealthProber(ctx context.Context) {
 				if target.Hot {
 					interval = time.Duration(s.cfg.RouteProbeHotIntervalSeconds) * time.Second
 				}
-				states[profile.Key] = routeProbeState{next: now.Add(interval), lastRequestObserved: requestedAt}
-				go s.probeRouteTarget(ctx, target, profile)
+				select {
+				case probeSlots <- struct{}{}:
+					states[profile.Key] = routeProbeState{next: now.Add(interval), lastRequestObserved: requestedAt}
+				case <-ctx.Done():
+					return
+				default:
+					continue
+				}
+				go func(target store.RouteProbeTarget, profile executionpool.RouteProfile) {
+					defer func() { <-probeSlots }()
+					s.probeRouteTarget(ctx, target, profile)
+				}(target, profile)
 			}
 		}
 	}
 }
 
 func (s *Service) probeRouteTarget(ctx context.Context, target store.RouteProbeTarget, profile executionpool.RouteProfile) {
-	leadership, locked, err := s.coordinationStore.TryAcquireRouteProbeLeadership(ctx, s.cfg.ExecutionPoolID, profile.Key)
+	leaseToken, locked, err := s.coordinationStore.TryClaimRouteProbe(ctx, s.cfg.ExecutionPoolID, profile.Key, time.Duration(s.cfg.RouteProbeTimeoutMS)*time.Millisecond+5*time.Second)
 	if err != nil || !locked {
 		return
 	}
-	defer leadership.Release()
+	defer func() {
+		releaseCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+		if err := s.coordinationStore.ReleaseRouteProbe(releaseCtx, s.cfg.ExecutionPoolID, profile.Key, leaseToken); err != nil {
+			s.logRouteProbeFailure("release_lease", err)
+		}
+	}()
 	client, err := s.httpClientForCandidate(target.Candidate, false, "")
 	if err != nil {
 		s.logRouteProbeFailure("prepare_client", err)