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/app/market/__init__.py

@@ -3,14 +3,30 @@ from __future__ import annotations
 from app.config import Settings
 from app.market.base import MarketData
 from app.market.binance import BinanceMarketData
+from app.market.coinbase import CoinbaseMarketData
 from app.market.fake import FakeMarketData
+from app.market.kraken import KrakenMarketData
+
+_FEEDS: dict[str, type[MarketData]] = {
+    "binance": BinanceMarketData,
+    "binanceus": BinanceMarketData,
+    "kraken": KrakenMarketData,
+    "coinbase": CoinbaseMarketData,
+}
 
 
 def build_market_data(settings: Settings) -> MarketData:
-    exchange = settings.exchange.lower()
-    if exchange in {"binance", "binanceus"}:
-        return BinanceMarketData()
-    raise ValueError(f"unsupported exchange: {settings.exchange}")
+    try:
+        feed_cls = _FEEDS[settings.exchange.lower()]
+    except KeyError:
+        raise ValueError(
+            f"unsupported exchange: {settings.exchange}. available: {sorted(_FEEDS)}"
+        ) from None
+    return feed_cls()
 
 
-__all__ = ["FakeMarketData", "MarketData", "build_market_data"]
+__all__ = [
+    "FakeMarketData",
+    "MarketData",
+    "build_market_data",
+]