P3.2+P3.3+P3.4: NODA1 node-worker + NATS auth config + Prometheus counters

P3.2 — Multi-node deployment:
- Added node-worker service to docker-compose.node1.yml (NODE_ID=noda1)
- NCS NODA1 now has NODE_WORKER_URL for metrics collection
- Fixed NODE_ID consistency: router NODA1 uses 'noda1'
- NODA2 node-worker/NCS gets NCS_REPORT_URL for latency reporting

P3.3 — NATS accounts/auth (opt-in config):
- config/nats-server.conf with 3 accounts: SYS, FABRIC, APP
- Per-user topic permissions (router, ncs, node_worker)
- Leafnode listener :7422 with auth
- Not yet activated (requires credential provisioning)

P3.4 — Prometheus counters:
- Router /fabric_metrics: caps_refresh, caps_stale, model_select,
  offload_total, breaker_state, score_ms histogram
- Node Worker /prom_metrics: jobs_total, inflight gauge, latency_ms histogram
- NCS /prom_metrics: runtime_health, runtime_p50/p95, node_wait_ms
- All bound to 127.0.0.1 (not externally exposed)

Made-with: Cursor

services/node-worker/fabric_metrics.py

@@ -0,0 +1,50 @@
+"""Prometheus metrics for Node Worker."""
+import logging
+
+logger = logging.getLogger("worker_metrics")
+
+try:
+    from prometheus_client import Counter, Gauge, Histogram, CollectorRegistry, generate_latest
+    PROM_AVAILABLE = True
+    REGISTRY = CollectorRegistry()
+
+    jobs_total = Counter(
+        "node_worker_jobs_total", "Jobs processed",
+        ["type", "status"], registry=REGISTRY,
+    )
+    inflight_gauge = Gauge(
+        "node_worker_inflight", "Currently inflight jobs",
+        registry=REGISTRY,
+    )
+    latency_hist = Histogram(
+        "node_worker_latency_ms", "Job latency in ms",
+        ["type", "model"],
+        buckets=[100, 250, 500, 1000, 2500, 5000, 15000, 30000],
+        registry=REGISTRY,
+    )
+
+except ImportError:
+    PROM_AVAILABLE = False
+    REGISTRY = None
+    logger.info("prometheus_client not installed, worker metrics disabled")
+
+
+def inc_job(req_type: str, status: str):
+    if PROM_AVAILABLE:
+        jobs_total.labels(type=req_type, status=status).inc()
+
+
+def set_inflight(count: int):
+    if PROM_AVAILABLE:
+        inflight_gauge.set(count)
+
+
+def observe_latency(req_type: str, model: str, latency_ms: int):
+    if PROM_AVAILABLE:
+        latency_hist.labels(type=req_type, model=model).observe(latency_ms)
+
+
+def get_metrics_text():
+    if PROM_AVAILABLE and REGISTRY:
+        return generate_latest(REGISTRY)
+    return None