feat: log OBD speed before GPS fix so rolling starts aren't lost

- _log_loop: when GPS has no fix but OBD speed > 1, write speed-only rows
  (NULL coordinates) instead of dropping the motion
- insert_tracking: accept None gps_x/gps_y -> NULL GPSX/GPSY
- app_trip: keep NULL-coord rows through normalize; _segment returns 0 for
  missing coords; route_points drops them (no position to draw)
- tests: speed-only rows build a trip with max speed + zero distance
- docs: FEAT-12 + readme note; server already filters NULL-GPS safely

modules/app_trip.py

@@ -47,9 +47,11 @@ def normalize_tracking_rows(rows):
         longitude = _number(row[3])
         speed = _number(row[4]) or 0
         odometer = _number(row[5]) if len(row) > 5 else None
-        if timestamp is None or latitude is None or longitude is None:
+        if timestamp is None:
             continue
-        if not (-90 <= latitude <= 90 and -180 <= longitude <= 180):
+        if latitude is not None and not (-90 <= latitude <= 90):
+            continue
+        if longitude is not None and not (-180 <= longitude <= 180):
             continue
         normalized.append({
             "id": int(row[0]),
@@ -66,6 +68,11 @@ def _segment(row, previous):
     seconds = (row["datetime"] - previous["datetime"]).total_seconds()
     if seconds <= 0:
         return 0, 0
+    if (
+        previous["latitude"] is None or previous["longitude"] is None
+        or row["latitude"] is None or row["longitude"] is None
+    ):
+        return 0, 0
     distance_km = haversine_km(
         (previous["latitude"], previous["longitude"]),
         (row["latitude"], row["longitude"]),
@@ -218,6 +225,9 @@ def build_trip_summaries(raw_rows):
 
 def route_points(raw_rows, max_points=2000, odometer_baseline=0.0, prior_km=0.0):
     rows = normalize_tracking_rows(raw_rows)
+    # The route polyline needs coordinates — drop speed-only rows logged before
+    # the first GPS fix (no position to draw; they add 0 distance anyway).
+    rows = [r for r in rows if r["latitude"] is not None and r["longitude"] is not None]
     filtered_rows = []
     for row in rows:
         if filtered_rows: