Add FastAPI backend for energy trading system

Implements FastAPI backend with ML model support for energy trading,
including price prediction models and RL-based battery trading policy.
Features dashboard, trading, backtest, and settings API routes with
WebSocket support for real-time updates.

backend/app/tasks/__init__.py

@@ -0,0 +1,4 @@
+from app.tasks.backtest_tasks import run_backtest_task
+from app.tasks.training_tasks import train_model_task
+
+__all__ = ["run_backtest_task", "train_model_task"]