fix(fabric): use broadcast subject for NATS capabilities discovery

NATS wildcards (node.*.capabilities.get) only work for subscriptions,
not for publish. Switch to a dedicated broadcast subject
(fabric.capabilities.discover) that all NCS instances subscribe to,
enabling proper scatter-gather discovery across nodes.

Made-with: Cursor

services/router/global_capabilities_client.py

@@ -26,7 +26,7 @@ CACHE_TTL = int(os.getenv("GLOBAL_CAPS_TTL", "30"))
 NATS_DISCOVERY_TIMEOUT_MS = int(os.getenv("NATS_DISCOVERY_TIMEOUT_MS", "500"))
 NATS_ENABLED = os.getenv("ENABLE_GLOBAL_CAPS_NATS", "true").lower() in ("true", "1")
 
-CAPS_DISCOVERY_SUBJECT = "node.*.capabilities.get"
+CAPS_DISCOVERY_SUBJECT = "fabric.capabilities.discover"
 CAPS_INBOX_PREFIX = "_CAPS_REPLY"
 
 _node_cache: Dict[str, Dict[str, Any]] = {}