Observability: Prometheus metrics, log panel, runbook

- GET /api/metrics renders Prometheus text (equity, P&L, per-strategy
  equity/pnl/allocation/halted, info) with no client library.
- In-memory ring log handler (app/logs.py) exposed at GET /api/logs and a
  dashboard "Server logs" panel; Runtime mirrors bot events into the logger.
- docs/runbook.md covers deploys, the kill switch, resetting paper state and
  going live. Adds tests for metrics rendering and the log ring.

frontend/src/api.js

@@ -12,6 +12,8 @@ export const getPositions = () => http.get('/positions').then((r) => r.data)
 export const getOrders = () => http.get('/orders').then((r) => r.data)
 export const getEvents = () => http.get('/events').then((r) => r.data)
 export const getEquity = () => http.get('/equity').then((r) => r.data)
+export const getLogs = (limit = 100) =>
+  http.get('/logs', { params: { limit } }).then((r) => r.data)
 
 export const startBot = (payload) => http.post('/bot/start', payload).then((r) => r.data)
 export const stopBot = () => http.post('/bot/stop').then((r) => r.data)