Adds GET /api/v1/admin/ops/ws/requests — a fan-out WebSocket that pushes
per-request metadata (method, path, model, account_id, status, latency_ms)
to all connected admin clients the moment each gateway dispatch completes.
- service/request_event_bus.go: lock-free pub/sub with non-blocking drop
when per-subscriber buffer (64 slots) is full; nil-safe Publish
- service/request_event_bus_test.go: 6 tests (basic, fanout, drop, nil, close)
- GatewayHandler: records reqStartTime at entry; defer emits RequestEvent on
every return; sets status success/error/rate_limited in both Gemini and
Anthropic dispatch paths
- OpsHandler: accepts *RequestEventBus; wires it to RequestStreamWSHandler
- ops_ws_requests_handler.go: subscribes to bus, pushes JSON per event,
reuses existing upgrader/conn-limit/ping-pong infrastructure
- Route: ws.GET("/requests", ...) alongside existing /ws/qps
- wire_gen.go: requestEventBus shared between OpsHandler and GatewayHandler
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