fix: trip builder handles NULL-GPS speed-only rows (BUG-16 follow-up)

Trips starting/ending on speed-only rows violated the trips.*GPSX NOT NULL
constraint. Use the first/last GPS-bearing row for start/end coordinates, and
skip a trip that never got any GPS fix (no location to record).

modules/app_trip.py

@@ -198,16 +198,28 @@ def build_trip_summaries(raw_rows):
         if not any(event["obd"] for event in events) and duration_seconds < 10:
             continue
 
+        # Speed-only rows (logged before the first GPS fix) have NULL coords.
+        # Use the first/last row that actually has a position for start/end GPS,
+        # and skip a trip that never got any fix at all (no location to record).
+        gps_rows = [
+            r for r in trip_rows
+            if r["latitude"] is not None and r["longitude"] is not None
+        ]
+        if not gps_rows:
+            continue
+        start_gps = gps_rows[0]
+        end_gps = gps_rows[-1]
+
         trips.append({
             "id": start["id"],
             "start_tracking_id": start["id"],
             "end_tracking_id": end["id"],
             "start_datetime": start["datetime"].isoformat(sep=" "),
             "end_datetime": end["datetime"].isoformat(sep=" "),
-            "start_gpsx": start["latitude"],
-            "start_gpsy": start["longitude"],
-            "end_gpsx": end["latitude"],
-            "end_gpsy": end["longitude"],
+            "start_gpsx": start_gps["latitude"],
+            "start_gpsy": start_gps["longitude"],
+            "end_gpsx": end_gps["latitude"],
+            "end_gpsy": end_gps["longitude"],
             "distance_km": round(distance_km, 3),
             "duration_seconds": duration_seconds,
             "point_count": len(trip_rows),