refactor: address python review findings

- Move FRED credential registration to FastAPI lifespan (was fragile
  import-order-dependent side-effect)
- Add noqa E402 annotations for imports after curl_cffi patch
- Fix all return type hints: bare dict -> dict[str, Any]
- Move yfinance import to module level (was inline in functions)
- Fix datetime.now() -> datetime.now(tz=timezone.utc) in openbb_service
- Add try/except error handling to Group B service functions
- Fix dict mutation in relative_rotation (immutable pattern)
- Extract _classify_rrg_quadrant helper function
- Fix type builtin shadow in routes_economy (type -> gdp_type)
- Fix falsy int guard (if year: -> if year is not None:)
- Remove user input echo from error messages

economy_service.py

@@ -174,7 +174,7 @@ async def get_fomc_documents(year: int | None = None) -> list[dict[str, Any]]:
     """Get FOMC meeting documents (minutes, projections, etc.)."""
     try:
         kwargs: dict[str, Any] = {"provider": "federal_reserve"}
-        if year:
+        if year is not None:
             kwargs["year"] = year
         result = await asyncio.to_thread(
             obb.economy.fomc_documents, **kwargs