Crypto trading bot: engine, brokers, backtester, dashboard, deploy

FastAPI backend with a single-strategy async engine, paper and Binance
brokers, pure-python indicators, a backtester that shares the engine's
portfolio math, and a Vue dashboard with a live WebSocket feed. Adds the
Gitea Actions CI/CD workflow that deploys to Traefik via docker_default.

backend/app/backtest/__init__.py

@@ -0,0 +1,6 @@
+from __future__ import annotations
+
+from app.backtest.backtester import Backtester
+from app.backtest.metrics import compute_metrics, max_drawdown_pct, sharpe_ratio
+
+__all__ = ["Backtester", "compute_metrics", "max_drawdown_pct", "sharpe_ratio"]