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/tests/undo.test.js

@@ -108,15 +108,22 @@ describe('Undo: Editor Save', () => {
         bodyEl.value = 'after edit';
         bodyEl.dispatchEvent(new Event('input', { bubbles: true }));
         click('#modal-save-close');
-        await sleep(400);
 
-        let card = (await fetch(`api/cards?ids=${res.id}`).then(r => r.json())).find(c => c.id == res.id);
+        let card;
+        for (let i = 0; i < 40; i++) {
+            await sleep(100);
+            card = (await fetch(`api/cards?ids=${res.id}`).then(r => r.json())).find(c => c.id == res.id);
+            if ((card?.body || '').includes('after edit')) break;
+        }
         expect(card.body).toContain('after edit');
 
         ctrlZ();
-        await sleep(400);
 
-        card = (await fetch(`api/cards?ids=${res.id}`).then(r => r.json())).find(c => c.id == res.id);
+        for (let i = 0; i < 40; i++) {
+            await sleep(100);
+            card = (await fetch(`api/cards?ids=${res.id}`).then(r => r.json())).find(c => c.id == res.id);
+            if ((card?.body || '').includes('before edit')) break;
+        }
         expect(card.body).toContain('before edit');
     });