Fix revenue endpoint 500 — rollback SQLAlchemy session after caught exceptions

When forecast_covers_range or forecast_revenue_for_date throw DB exceptions,
the swallowed exception leaves the async session in an aborted transaction state.
Subsequent queries (DOW averages, per-date accom) then fail with
InFailedSQLTransactionError. Adding db.rollback() in the except blocks
resets the session so the fallback path can continue cleanly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/api/public.py

@@ -384,6 +384,7 @@ async def get_revenue_forecast(
         covers_by_date = {c["date"]: c for c in covers_data.get("data", [])}
     except Exception as e:
         logger.warning(f"Covers forecast failed: {e}")
+        await db.rollback()
         covers_by_date = {}
 
     # DOW averages from recent 8 weeks — fallback when covers gives zero for future dates
@@ -446,6 +447,7 @@ async def get_revenue_forecast(
                 accom_forecast = accom_otb + accom_pickup
                 accom_prior_otb = accom_forecast_data.get('prior_year_otb_rev', 0) or 0
             except Exception:
+                await db.rollback()
                 accom_otb = accom_forecast = accom_prior_otb = 0
 
             # Restaurant