refactor: address architect review findings (6 items)

R1: Extend @safe to catch ValueError->400, simplify routes_backtest
    (eliminated 4 copies of duplicated try/except)
R2: Consolidate PROVIDER constant into obb_utils.py (single source)
R3: Add days_ago() helper to obb_utils.py, replace 8+ duplications
R4: Extract Reddit/ApeWisdom into reddit_service.py from finnhub_service
R5: Fix missing top-level import asyncio in finnhub_service
R6: (deferred - sentiment logic extraction is a larger change)

All 561 tests passing.

obb_utils.py

@@ -66,11 +66,16 @@ def first_or_empty(result: Any) -> dict[str, Any]:
     return items[0] if items else {}
 
 
+def days_ago(days: int) -> str:
+    """Return a YYYY-MM-DD date string for N days ago (UTC)."""
+    return (datetime.now(tz=timezone.utc) - timedelta(days=days)).strftime("%Y-%m-%d")
+
+
 async def fetch_historical(
     symbol: str, days: int = 365, provider: str = PROVIDER,
 ) -> Any | None:
     """Fetch historical price data, returning the OBBject result or None."""
-    start = (datetime.now(tz=timezone.utc) - timedelta(days=days)).strftime("%Y-%m-%d")
+    start = days_ago(days)
     try:
         result = await asyncio.to_thread(
             obb.equity.price.historical, symbol, start_date=start, provider=provider,