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/__init__.py

@@ -0,0 +1,3 @@
+from tests.conftest import sample_price_data, sample_battery_state
+
+__all__ = ["sample_price_data", "sample_battery_state"]

backend/tests/test_api/test_backtest.py

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+import pytest
+
+
+def test_backtest_start():
+    pass
+
+
+def test_backtest_status():
+    pass
+
+
+def test_backtest_history():
+    pass

backend/tests/test_api/test_dashboard.py

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+import pytest
+from fastapi.testclient import TestClient
+
+
+def test_health_check(client: TestClient):
+    response = client.get("/health")
+    assert response.status_code == 200
+    assert response.json()["status"] == "healthy"
+
+
+def test_dashboard_summary(client: TestClient):
+    response = client.get("/api/v1/dashboard/summary")
+    assert response.status_code == 200
+
+
+def test_latest_prices(client: TestClient):
+    response = client.get("/api/v1/dashboard/prices")
+    assert response.status_code == 200
+    assert "regions" in response.json()
+
+
+def test_battery_states(client: TestClient):
+    response = client.get("/api/v1/dashboard/battery")
+    assert response.status_code == 200
+    assert "batteries" in response.json()
+
+
+def test_arbitrage_opportunities(client: TestClient):
+    response = client.get("/api/v1/dashboard/arbitrage")
+    assert response.status_code == 200
+    assert "opportunities" in response.json()
+
+
+def test_get_settings(client: TestClient):
+    response = client.get("/api/v1/settings")
+    assert response.status_code == 200
+
+
+def test_list_models(client: TestClient):
+    response = client.get("/api/v1/models")
+    assert response.status_code == 200
+
+
+def test_get_strategies(client: TestClient):
+    response = client.get("/api/v1/trading/strategies")
+    assert response.status_code == 200

backend/tests/test_api/test_models.py

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+import pytest
+
+
+def test_model_prediction():
+    pass
+
+
+def test_model_training():
+    pass

backend/tests/test_api/test_trading.py

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+import pytest
+
+
+def test_strategy_toggle():
+    pass
+
+
+def test_trading_positions():
+    pass