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.

backend/tests/test_observability.py

@@ -0,0 +1,107 @@
+from __future__ import annotations
+
+import logging
+
+from app.logs import RingLogHandler
+from app.metrics import render_metrics
+from app.schemas import MultiStatusOut, StrategyStatusOut
+
+
+def make_status(**overrides) -> MultiStatusOut:
+    strategy = StrategyStatusOut(
+        strategy_key="sma_cross",
+        strategy_name="SMA Crossover",
+        params={},
+        symbol="BTC/USDT",
+        timeframe="5m",
+        allocation=0.5,
+        cash=5000,
+        equity=5100,
+        realized_pnl=100,
+        unrealized_pnl=0,
+        total_pnl=100,
+        open_positions=1,
+        halted=False,
+        trades_today=2,
+    )
+    base = {
+        "running": True,
+        "mode": "paper",
+        "exchange": "binance",
+        "price": 100.0,
+        "starting_balance": 10000,
+        "equity": 10100,
+        "total_pnl": 100,
+        "strategies": [strategy],
+    }
+    base.update(overrides)
+    return MultiStatusOut(**base)
+
+
+def test_render_metrics_contains_core_series() -> None:
+    body = render_metrics(make_status(), "paper", "binance")
+    assert "crypto_running 1" in body
+    assert "crypto_equity 10100" in body
+    assert "crypto_total_pnl 100" in body
+    assert "crypto_open_positions 1" in body
+    assert 'crypto_strategy_equity{strategy="sma_cross",symbol="BTC/USDT"} 5100' in body
+    assert 'crypto_strategy_allocation{strategy="sma_cross"} 0.5' in body
+    assert 'crypto_info{mode="paper",exchange="binance"} 1' in body
+
+
+def test_render_metrics_omits_price_when_none() -> None:
+    body = render_metrics(make_status(price=None), "paper", "binance")
+    assert "crypto_price" not in body
+
+
+def test_ring_log_handler_captures() -> None:
+    handler = RingLogHandler(capacity=5)
+    logger = logging.getLogger("test.ring")
+    logger.addHandler(handler)
+    logger.setLevel(logging.INFO)
+    try:
+        logger.info("hello %s", "world")
+        entries = handler.snapshot()
+        assert entries[-1]["message"] == "hello world"
+        assert entries[-1]["level"] == "info"
+    finally:
+        logger.removeHandler(handler)
+
+
+def test_ring_log_handler_respects_capacity() -> None:
+    handler = RingLogHandler(capacity=3)
+    logger = logging.getLogger("test.ring.cap")
+    logger.addHandler(handler)
+    logger.setLevel(logging.INFO)
+    try:
+        for i in range(10):
+            logger.info("m%d", i)
+        entries = handler.snapshot()
+        assert len(entries) == 3
+        assert entries[-1]["message"] == "m9"
+    finally:
+        logger.removeHandler(handler)
+
+
+def test_metrics_endpoint(runtime) -> None:
+    from fastapi.testclient import TestClient
+
+    from app.main import create_app
+
+    app = create_app(runtime.settings, runtime)
+    with TestClient(app) as client:
+        response = client.get("/api/metrics")
+        assert response.status_code == 200
+        assert "crypto_running" in response.text
+
+
+def test_logs_endpoint(runtime) -> None:
+    from fastapi.testclient import TestClient
+
+    from app.main import create_app
+
+    app = create_app(runtime.settings, runtime)
+    with TestClient(app) as client:
+        response = client.get("/api/logs")
+        assert response.status_code == 200
+        assert "entries" in response.json()