fixes: collab move, caldav abort, draft recovery, autobackup, test stabilization

- Collab: moving a shared card to a local bucket no longer deletes it
  (clear relay_uid before tombstone echo returns)
- CalDAV: abort sync on remote fetch failure instead of treating all
  local cards as remotely-deleted
- Editor: autobackup drafts to localStorage with restore prompt on
  re-open (skipped during tests)
- Cards POST: persist scratchpad and due_date (was dropped on create)
- Disable spellcheck/autocorrect on editor inputs
- Test runner: purge leftover __prefix__ cards/buckets + editor drafts
  before every run (cleans up from failed previous runs)
- Stabilize mark-done, group-delete, undo-body tests with poll loops

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/plugins/collab-buckets/backend.php

@@ -411,9 +411,16 @@ function collabSyncCards(PDO $db): array {
         $stats['moved']++;
 
         if ($mv['card_missing'] || empty($mv['new_bucket_uid'])) {
-            // Card is gone or moved out of collab entirely — forget about it
+            // Card is gone or moved out of collab entirely — forget about it.
+            // Critical: also clear the card's relay_uid so the incoming
+            // tombstone (echoed back from the relay on next pull) doesn't
+            // find this card and delete it locally too.
             $db->prepare('DELETE FROM collab_card_state WHERE card_id = :id')
                 ->execute(['id' => $mv['card_id']]);
+            if (!$mv['card_missing']) {
+                $db->prepare('UPDATE cards SET relay_uid = NULL WHERE id = :id')
+                    ->execute(['id' => $mv['card_id']]);
+            }
         } else {
             // Card moved to a different collab bucket. Rewrite state so the
             // push phase below picks it up under the new bucket_uid and also