fix(plex): a collection created on Plex keeps its editable row when the refresh read fails

The rollback dropped the new row: the next sync recreated it read-only, out of every 'add to' list, and the duplicate-name check let a retry make a second same-named collection on Plex.

backend/app/routes/plex/collections.py

@@ -454,16 +454,25 @@ def create_collection(
         raise not_found("library")
     _reject_duplicate_name(db, lib.id, title)
     wrote = False
+    new_rk = ""
     try:
         with PlexClient(db) as plex:
             # A show collection is made as one (Plex type 2): as a movie one it stayed empty.
             new = plex.create_collection(lib.plex_key, title, seed, 2 if seed_show else 1)
             wrote = True
-            col = plex_sync.resync_collection(db, plex, lib, str(new.get("ratingKey")))
+            new_rk = str(new.get("ratingKey") or "")
+            col = plex_sync.resync_collection(db, plex, lib, new_rk)
             col.editable = True
         db.commit()
     except (PlexError, PlexNotConfigured) as e:
         db.rollback()
+        if wrote and new_rk:
+            # It is on Plex now, and only the follow-up read failed. Its row is kept, editable: the
+            # full sync preserves `editable` but creates a missing row read-only, so the collection
+            # would drop out of every "add to" list; and the duplicate-name check reads these rows,
+            # so a retry of the same name would make a second one on Plex.
+            db.add(PlexCollection(rating_key=new_rk, library_id=lib.id, title=title, editable=True))
+            db.commit()
         raise _write_or_pending_error(wrote, e) from e
     return _collection_card(col)