feat: add portfolio optimization and congress tracking (TDD)

Portfolio optimization (3 endpoints):
- POST /portfolio/optimize - HRP optimal weights via scipy clustering
- POST /portfolio/correlation - pairwise correlation matrix
- POST /portfolio/risk-parity - inverse-volatility risk parity weights

Congress tracking (2 endpoints):
- GET /regulators/congress/trades - congress member stock trades
- GET /regulators/congress/bills?query= - search congress bills

Implementation:
- portfolio_service.py: HRP with scipy fallback to inverse-vol
- congress_service.py: multi-provider fallback pattern
- 51 new tests (14 portfolio unit, 20 portfolio route, 12 congress
  unit, 7 congress route)
- All 312 tests passing

tests/test_routes_congress.py

@@ -0,0 +1,98 @@
+"""Tests for congress trading routes (TDD - RED phase first)."""
+
+from unittest.mock import patch, AsyncMock
+
+import pytest
+from httpx import AsyncClient, ASGITransport
+
+from main import app
+
+
+@pytest.fixture
+async def client():
+    transport = ASGITransport(app=app)
+    async with AsyncClient(transport=transport, base_url="http://test") as c:
+        yield c
+
+
+# --- GET /api/v1/regulators/congress/trades ---
+
+
+@pytest.mark.asyncio
+@patch("routes_regulators.congress_service.get_congress_trades", new_callable=AsyncMock)
+async def test_congress_trades_happy_path(mock_fn, client):
+    mock_fn.return_value = [
+        {
+            "representative": "Nancy Pelosi",
+            "ticker": "NVDA",
+            "transaction_date": "2024-01-15",
+            "transaction_type": "Purchase",
+            "amount": "$1,000,001-$5,000,000",
+        }
+    ]
+    resp = await client.get("/api/v1/regulators/congress/trades")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["success"] is True
+    assert len(data["data"]) == 1
+    assert data["data"][0]["representative"] == "Nancy Pelosi"
+    mock_fn.assert_called_once()
+
+
+@pytest.mark.asyncio
+@patch("routes_regulators.congress_service.get_congress_trades", new_callable=AsyncMock)
+async def test_congress_trades_empty(mock_fn, client):
+    mock_fn.return_value = []
+    resp = await client.get("/api/v1/regulators/congress/trades")
+    assert resp.status_code == 200
+    assert resp.json()["data"] == []
+
+
+@pytest.mark.asyncio
+@patch("routes_regulators.congress_service.get_congress_trades", new_callable=AsyncMock)
+async def test_congress_trades_service_error_returns_502(mock_fn, client):
+    mock_fn.side_effect = RuntimeError("Data provider unavailable")
+    resp = await client.get("/api/v1/regulators/congress/trades")
+    assert resp.status_code == 502
+
+
+# --- GET /api/v1/regulators/congress/bills ---
+
+
+@pytest.mark.asyncio
+@patch("routes_regulators.congress_service.search_congress_bills", new_callable=AsyncMock)
+async def test_congress_bills_happy_path(mock_fn, client):
+    mock_fn.return_value = [
+        {"title": "Infrastructure Investment and Jobs Act", "bill_id": "HR3684"},
+        {"title": "Inflation Reduction Act", "bill_id": "HR5376"},
+    ]
+    resp = await client.get("/api/v1/regulators/congress/bills?query=infrastructure")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["success"] is True
+    assert len(data["data"]) == 2
+    assert data["data"][0]["bill_id"] == "HR3684"
+    mock_fn.assert_called_once_with("infrastructure")
+
+
+@pytest.mark.asyncio
+async def test_congress_bills_missing_query(client):
+    resp = await client.get("/api/v1/regulators/congress/bills")
+    assert resp.status_code == 422
+
+
+@pytest.mark.asyncio
+@patch("routes_regulators.congress_service.search_congress_bills", new_callable=AsyncMock)
+async def test_congress_bills_empty(mock_fn, client):
+    mock_fn.return_value = []
+    resp = await client.get("/api/v1/regulators/congress/bills?query=nonexistent")
+    assert resp.status_code == 200
+    assert resp.json()["data"] == []
+
+
+@pytest.mark.asyncio
+@patch("routes_regulators.congress_service.search_congress_bills", new_callable=AsyncMock)
+async def test_congress_bills_service_error_returns_502(mock_fn, client):
+    mock_fn.side_effect = RuntimeError("Congress API unavailable")
+    resp = await client.get("/api/v1/regulators/congress/bills?query=tax")
+    assert resp.status_code == 502