fix: BUG-21 GPS-speed fallback in server route replay

BUGS.md

@@ -35,11 +35,13 @@ When CLOSED, move the entire entry to Resolved — don't duplicate.
   (`insert_tracking(gps_x, gps_y, speed=None, …)`) — there is no GPS-derived speed fallback, so
   the SPEED column stays NULL and the replay shows 0.0 km/h (`speed_source="gps"`).
 - **Data**: trip #9 has 723 points — 570 with OBD speed, 25 with speed=0, 128 with NULL speed.
-- **Fix (proposed)**:
-  1. GPS-speed fallback in `_log_loop()` — when OBD speed is None/0 but GPS coords exist,
-     compute speed from the previous position (haversine / elapsed time) and log that as SPEED,
-     so the replay shows the real speed (sourced "gps").
-  2. Investigate why the OBD adapter didn't recover for ~20 min (reconnect on stalled reads).
+- **Fix**: mirror the Pi's `route_points` GPS-speed fallback in the server's `get_trip_route()`
+  (`server/modules/db.py`) — when OBD speed is missing, derive speed from the previous point's
+  movement (haversine / elapsed time, ≥8 m, ≤220 km/h) so the replay shows the real speed
+  instead of flatlining at 0 km/h. (The Pi's own replay already did this; only the portal was
+  missing it.)
+- **Follow-up**: investigate why the OBD adapter didn't recover for ~20 min (reconnect on
+  stalled reads).
 
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