feat(trading): add trade history and daily FIFO retention cron

- trading_trades table (migration 0001) persists every buy/sell via optional onTrade callback
- /history [n] command shows caller's last N trades (default 10, max 50), HTML-escaped
- daily cron at 0 17 * * * trims to 1000/user + 10000/global via FIFO delete
- persistence failure logs but does not fail the trade reply

src/modules/trading/migrations/0001_trades.sql

@@ -0,0 +1,11 @@
+CREATE TABLE trading_trades (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  user_id INTEGER NOT NULL,
+  symbol TEXT NOT NULL,
+  side TEXT NOT NULL CHECK (side IN ('buy','sell')),
+  qty INTEGER NOT NULL,
+  price_vnd INTEGER NOT NULL,
+  ts INTEGER NOT NULL
+);
+CREATE INDEX idx_trading_trades_user_ts ON trading_trades(user_id, ts DESC);
+CREATE INDEX idx_trading_trades_ts ON trading_trades(ts);