Risk controls, alerts, API token, more exchanges, presets

- RiskManager halts + flattens on max daily loss / drawdown, caps position
  size and trades per day; adds a manual kill switch (POST /api/bot/kill).
- Telegram and webhook notifications on trades, errors and halts.
- Optional API bearer token on /api, injected server-side by the frontend
  nginx so the browser never sees it.
- Kraken and Coinbase market data (public); Coinbase live broker. Live on an
  unsupported exchange now errors instead of silently falling back to paper.
- Strategy presets backed by the StrategyConfig table (CRUD API + UI).
- Idempotent additive-column migration so existing SQLite databases upgrade in
  place (fixes the new strategy_configs.name column).

backend/tests/test_exchanges.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+import pytest
+
+from app.config import Settings
+from app.market.coinbase import CoinbaseMarketData, to_product_id
+from app.market.kraken import KrakenMarketData
+
+
+def test_symbol_mapping() -> None:
+    assert to_product_id("BTC/USDT") == "BTC-USDT"
+    assert to_product_id("eth/usd") == "ETH-USD"
+
+
+def test_kraken_interval_mapping() -> None:
+    assert KrakenMarketData._interval("1h") == 60
+    assert KrakenMarketData._interval("1d") == 1440
+    with pytest.raises(ValueError):
+        KrakenMarketData._interval("2m")
+
+
+def test_coinbase_granularity_mapping() -> None:
+    assert CoinbaseMarketData._granularity("1m") == 60
+    assert CoinbaseMarketData._granularity("1d") == 86400
+    with pytest.raises(ValueError):
+        CoinbaseMarketData._granularity("3m")
+
+
+def test_build_market_data_supports_exchanges() -> None:
+    from app.market import build_market_data
+
+    assert type(build_market_data(Settings(exchange="binance"))).__name__ == "BinanceMarketData"
+    assert type(build_market_data(Settings(exchange="kraken"))).__name__ == "KrakenMarketData"
+    assert type(build_market_data(Settings(exchange="coinbase"))).__name__ == "CoinbaseMarketData"
+
+
+def test_build_market_data_rejects_unknown() -> None:
+    from app.market import build_market_data
+
+    with pytest.raises(ValueError, match="unsupported exchange"):
+        build_market_data(Settings(exchange="ftx"))
+
+
+def test_build_broker_paper_default() -> None:
+    from app.broker import build_broker
+    from app.broker.paper import PaperBroker
+
+    assert isinstance(build_broker(Settings(mode="paper", exchange="kraken")), PaperBroker)
+
+
+def test_build_broker_live_unsupported_exchange() -> None:
+    from app.broker import build_broker
+
+    with pytest.raises(ValueError, match="not supported"):
+        build_broker(Settings(mode="live", exchange="kraken"))