Fix POI distance calculation reliability for remote/Celery execution

- Fix silent log loss: replace hardcoded "uvicorn.error" logger with __name__
  in osrm_client, otp_client, poi_distance_calculator, and poi_tasks (uvicorn
  logger has no handlers in Celery worker, so all errors were silently dropped)
- Add Celery retry: autoretry_for=(Exception,), max_retries=3, retry_backoff
- Add top-level exception handling in task with full traceback logging
- Fix upsert_distances: replace session.merge() (PK-based) with proper
  dialect-aware INSERT ON DUPLICATE KEY UPDATE / ON CONFLICT DO UPDATE
- Filter out listings with null/zero coordinates before routing
- Raise OSError when all routing engines fail with 0 results computed,
  distinguishing "nothing to compute" from "all engines unreachable"

services/poi_distance_calculator.py

@@ -15,7 +15,7 @@ from rec.otp_client import otp_transit_route
 from repositories.listing_repository import ListingRepository
 from repositories.poi_repository import POIRepository
 
-logger = logging.getLogger("uvicorn.error")
+logger = logging.getLogger(__name__)
 
 # Map travel mode names to OSRM profiles
 _OSRM_PROFILES = {
@@ -61,8 +61,25 @@ async def calculate_poi_distances(
         logger.info("No listings found for distance calculation")
         return 0
 
+    # Filter out listings without valid coordinates
+    valid_listings = [
+        l for l in listings
+        if l.latitude is not None and l.longitude is not None
+        and l.latitude != 0 and l.longitude != 0
+    ]
+    if len(valid_listings) < len(listings):
+        logger.warning(
+            f"Skipped {len(listings) - len(valid_listings)} listings "
+            f"with missing coordinates"
+        )
+    listings = valid_listings
+    if not listings:
+        logger.warning("No listings with valid coordinates")
+        return 0
+
     total_computed = 0
     total_modes = len(travel_modes)
+    modes_failed: list[str] = []
 
     for mode_idx, mode in enumerate(travel_modes):
         mode_upper = mode.upper()
@@ -105,6 +122,7 @@ async def calculate_poi_distances(
                 continue
         except (aiohttp.ClientError, OSError) as e:
             logger.error(f"Routing engine unreachable for {mode_upper}: {e}")
+            modes_failed.append(mode_upper)
             if on_progress:
                 on_progress(
                     total_computed, len(listings) * total_modes,
@@ -114,6 +132,13 @@ async def calculate_poi_distances(
 
         total_computed += computed
 
+    if modes_failed and total_computed == 0:
+        failed_str = ", ".join(modes_failed)
+        raise OSError(
+            f"All routing engines failed ({failed_str}). "
+            f"No distances computed for {len(listings)} listings."
+        )
+
     return total_computed