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/.env.example

@@ -0,0 +1,24 @@
+APP_NAME=Energy Trading API
+APP_VERSION=1.0.0
+DEBUG=true
+
+HOST=0.0.0.0
+PORT=8000
+
+DATA_PATH=~/energy-test-data/data/processed
+
+CORS_ORIGINS=http://localhost:3000,http://localhost:5173
+
+WS_HEARTBEAT_INTERVAL=30
+
+CELERY_BROKER_URL=redis://localhost:6379/0
+CELERY_RESULT_BACKEND=redis://localhost:6379/0
+
+MODELS_PATH=models
+RESULTS_PATH=results
+
+BATTERY_MIN_RESERVE=0.10
+BATTERY_MAX_CHARGE=0.90
+
+ARBITRAGE_MIN_SPREAD=5.0
+MINING_MARGIN_THRESHOLD=5.0