fix v1.41.2: uploaded files survive marker rebinding

- new WS houseplan/files/migrate moves /files/<oldId>/ to the new id
  (admin-only, sanitized ids, merge-safe, removes the empty old dir)
- _saveMarker calls it and rewrites pdf urls (migratePdfUrls pure
  helper, +1 unit test, 112) when rebinding changes the id
- field incident: the sauna heater manuals pointed at an orphaned
  old-id folder that got cleaned up; data restored by hand on the
  home instance (official Harvia PDFs re-downloaded)
- TESTING/CHANGELOG same-commit

package.json

@@ -1,6 +1,6 @@
 {
   "name": "houseplan-card",
-  "version": "1.41.1",
+  "version": "1.41.2",
   "description": "Interactive house plan Lovelace card for Home Assistant",
   "license": "MIT",
   "type": "module",