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/core/__init__.py

@@ -0,0 +1,25 @@
+from app.core.constants import (
+    DEFAULT_BATTERY_CAPACITY_MWH,
+    DEFAULT_CHARGE_RATE_MW,
+    DEFAULT_DISCHARGE_RATE_MW,
+    DEFAULT_EFFICIENCY,
+    WS_HEARTBEAT_INTERVAL,
+    PRICE_DATA_REGIONS,
+    DEFAULT_DATA_LIMIT,
+    BACKTEST_RESULT_TIMEOUT,
+    TRAINING_RESULT_TIMEOUT,
+    MAX_BACKTEST_TRADES,
+)
+
+__all__ = [
+    "DEFAULT_BATTERY_CAPACITY_MWH",
+    "DEFAULT_CHARGE_RATE_MW",
+    "DEFAULT_DISCHARGE_RATE_MW",
+    "DEFAULT_EFFICIENCY",
+    "WS_HEARTBEAT_INTERVAL",
+    "PRICE_DATA_REGIONS",
+    "DEFAULT_DATA_LIMIT",
+    "BACKTEST_RESULT_TIMEOUT",
+    "TRAINING_RESULT_TIMEOUT",
+    "MAX_BACKTEST_TRADES",
+]