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

main.py

@@ -1,4 +1,5 @@
 import logging
+from contextlib import asynccontextmanager
 
 import uvicorn
 from fastapi import FastAPI
@@ -12,41 +13,52 @@ import curl_cffi.requests as _cffi_requests
 
 _orig_session_init = _cffi_requests.Session.__init__
 
+
 def _patched_session_init(self, *args, **kwargs):
     if kwargs.get("impersonate") == "chrome":
         kwargs["impersonate"] = "safari"
     _orig_session_init(self, *args, **kwargs)
 
+
 _cffi_requests.Session.__init__ = _patched_session_init
 
-from openbb import obb
-from config import settings
+from openbb import obb  # noqa: E402 - must be after curl_cffi patch
 
-# Register optional provider credentials with OpenBB
-if settings.fred_api_key:
-    obb.user.credentials.fred_api_key = settings.fred_api_key
-from routes import router
-from routes_sentiment import router as sentiment_router
-from routes_macro import router as macro_router
-from routes_technical import router as technical_router
-from routes_quantitative import router as quantitative_router
-from routes_calendar import router as calendar_router
-from routes_market import router as market_router
-from routes_shorts import router as shorts_router
-from routes_fixed_income import router as fixed_income_router
-from routes_economy import router as economy_router
-from routes_surveys import router as surveys_router
-from routes_regulators import router as regulators_router
+from config import settings  # noqa: E402
+from routes import router  # noqa: E402
+from routes_calendar import router as calendar_router  # noqa: E402
+from routes_economy import router as economy_router  # noqa: E402
+from routes_fixed_income import router as fixed_income_router  # noqa: E402
+from routes_macro import router as macro_router  # noqa: E402
+from routes_market import router as market_router  # noqa: E402
+from routes_quantitative import router as quantitative_router  # noqa: E402
+from routes_regulators import router as regulators_router  # noqa: E402
+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
 
 logging.basicConfig(
     level=settings.log_level.upper(),
     format="%(asctime)s %(levelname)s %(name)s: %(message)s",
 )
+logger = logging.getLogger(__name__)
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Register provider credentials once at startup."""
+    if settings.fred_api_key:
+        obb.user.credentials.fred_api_key = settings.fred_api_key
+        logger.info("FRED API key registered")
+    yield
+
 
 app = FastAPI(
     title="OpenBB Investment Analysis API",
     version="0.1.0",
     description="REST API for stock data and rule-based investment analysis, powered by OpenBB SDK.",
+    lifespan=lifespan,
 )
 
 app.add_middleware(