Add backtesting entry point for offline strategy testing

Introduces a BacktestClient that replays historical 1-min bars against the
existing strategy code, plus a CLI entry point (npm run backtest) that fetches
bars from Alpaca and runs the bot over a date range. Makes wait() pluggable
so the backtest resolves delays instantly while advancing simulated time.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -16,7 +16,8 @@
     "dev": "nodemon --exec ts-node src/index.ts",
     "test": "vitest run",
     "test:watch": "vitest",
-    "lint": "eslint src/"
+    "lint": "eslint src/",
+    "backtest": "ts-node src/backtest.ts"
   },
   "dependencies": {
     "@alpacahq/alpaca-trade-api": "^3.1.3",