fix: prevent OOM on rapid schema publishing

Add concurrency-limited CosmoGenerator (semaphore limit=1, 60s timeout)
to prevent unbounded concurrent wgc process spawning. Add debouncer
(500ms) to coalesce rapid schema updates per org+ref. Fix double
subgraph fetch in Supergraph resolver and goroutine leak in
SchemaUpdates subscription.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/service/service.go

@@ -201,11 +201,13 @@ func start(closeEvents chan error, logger *slog.Logger, connectToAmqpFunc func(u
 		defer rootCancel()
 
 		resolver := &graph.Resolver{
-			EventStore: eventStore,
-			Publisher:  eventPublisher,
-			Logger:     logger,
-			Cache:      serviceCache,
-			PubSub:     graph.NewPubSub(),
+			EventStore:     eventStore,
+			Publisher:      eventPublisher,
+			Logger:         logger,
+			Cache:          serviceCache,
+			PubSub:         graph.NewPubSub(),
+			CosmoGenerator: graph.NewCosmoGenerator(&graph.DefaultCommandExecutor{}, 60*time.Second),
+			Debouncer:      graph.NewDebouncer(500 * time.Millisecond),
 		}
 
 		config := generated.Config{