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

main.py

@@ -37,6 +37,7 @@ from routes_sentiment import router as sentiment_router  # noqa: E402
 from routes_shorts import router as shorts_router  # noqa: E402
 from routes_surveys import router as surveys_router  # noqa: E402
 from routes_technical import router as technical_router  # noqa: E402
+from routes_portfolio import router as portfolio_router  # noqa: E402
 
 logging.basicConfig(
     level=settings.log_level.upper(),
@@ -81,6 +82,7 @@ app.include_router(fixed_income_router)
 app.include_router(economy_router)
 app.include_router(surveys_router)
 app.include_router(regulators_router)
+app.include_router(portfolio_router)
 
 
 @app.get("/health", response_model=dict[str, str])