osm merge, optmisation

FORMATS.md

@@ -104,7 +104,7 @@ Coordinates are `[lat, lng]`; the importer swaps to `[lng, lat]` internally. Gar
 - Non-finite or out-of-range lat/lng.
 - Jumps > 5 km between consecutive points.
 
-Stored only in memory (cleared by the **Loaded data → Clear** button or app restart).
+**Persisted in the SQLite database** (`video_metadata` table, keyed by `video_name`). Once imported, the polylines hydrate automatically on every app start — you don't have to re-pick the file each session. Cleared by the **Loaded data → Clear** button on the Per-video metadata row, or by **Reset DB** (which wipes the whole database).
 
 ### Metadata polyline (legacy single-track)
 Single-video legacy format used by the old FastAPI pipeline.