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/tests/test_api/test_models.py

@@ -0,0 +1,9 @@
+import pytest
+
+
+def test_model_prediction():
+    pass
+
+
+def test_model_training():
+    pass