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/App.vue

@@ -4,6 +4,7 @@ import * as api from './api'
 import BacktestPanel from './components/BacktestPanel.vue'
 import EquityChart from './components/EquityChart.vue'
 import EventLog from './components/EventLog.vue'
+import LogsPanel from './components/LogsPanel.vue'
 import MultiStrategyPanel from './components/MultiStrategyPanel.vue'
 import OrdersTable from './components/OrdersTable.vue'
 import PositionsTable from './components/PositionsTable.vue'
@@ -374,6 +375,8 @@ onUnmounted(() => {
       <EventLog :events="events" />
     </div>
 
+    <LogsPanel />
+
     <PositionsTable :positions="positions" @close="handleClose" />
     <OrdersTable :orders="orders" />