feat(ift): EventHub AI Router stack for Zed

FastAPI gateway with A/B/C lane orchestration, LiteLLM proxy config,
Swarm stack (postgres, redis, VPN off-by-default), deploy/smoke/audit scripts.

router/metrics.py

@@ -0,0 +1,31 @@
+"""Prometheus metrics for gateway tier/lane routing."""
+
+from __future__ import annotations
+
+from prometheus_client import CONTENT_TYPE_LATEST, Counter, Histogram, generate_latest
+
+REQUESTS = Counter(
+    "ai_router_requests_total",
+    "Total routed requests",
+    ["tier", "lane", "model", "status"],
+)
+ESCALATIONS = Counter(
+    "ai_router_escalations_total",
+    "Lane escalations",
+    ["from_lane", "to_lane", "reason"],
+)
+CLASSIFY = Counter(
+    "ai_router_classify_total",
+    "Classification results",
+    ["tier"],
+)
+DURATION = Histogram(
+    "ai_router_request_duration_seconds",
+    "Request duration",
+    ["tier", "model"],
+    buckets=(0.1, 0.25, 0.5, 1, 2, 5, 10, 30, 60, 120, 180),
+)
+
+
+def metrics_payload() -> tuple[bytes, str]:
+    return generate_latest(), CONTENT_TYPE_LATEST