fix(planner): eliminate drag-and-drop jank in trip planner

- Suppress trek-stagger animation on the day list while a drag is active
  so nth-child delays (0–320 ms) no longer re-fire on every hover change
- Replace sibling drop-indicator <div> injections with borderTop/borderBottom
  on the target row to prevent nth-child index shifts during drag
- Dedup setDragOverDayId calls in onDragOver handlers so setState is only
  invoked when the active day actually changes
- Move initTransportPositions out of getMergedItems (render path) into a
  useEffect to stop mid-drag setState cascades

.gitignore

@@ -58,4 +58,6 @@ coverage
 *.tgz
 
 .scannerwork
-test-data
+test-data
+
+.run