fixes: scratchpad, zen ESC, chat time, tooltip safety, collab sync race

- Scratchpad: card-scoped private notes in editor (toggle vs preview),
  smaller font, cleared via button, stored in cards.scratchpad
- Zen mode: ESC exits zen before closing detail, Z toggles zen
- Chat: always show absolute time (hh:mm, yesterday, or date+time)
- Backspace/Delete also deletes focused card (not just selected)
- Selected + focused cards use brand accent (not accent2)
- Tooltip: guard against non-element targets
- Collab sync: skip poll while editor is open, 2s push debounce
- Rrule test: only check geburtstag tag, not title format

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

public/plugins/collab-buckets/backend.php

@@ -436,7 +436,8 @@ function collabSyncCards(PDO $db): array {
         FROM cards c
         INNER JOIN buckets b ON b.id = c.bucket_id AND b.collab_uid IS NOT NULL
         LEFT JOIN collab_card_state cs ON cs.card_id = c.id
-        WHERE cs.last_push_at IS NULL OR c.updated_at > cs.last_push_at
+        WHERE (cs.last_push_at IS NULL OR c.updated_at > cs.last_push_at)
+          AND c.updated_at < datetime('now', '-2 seconds')
     ")->fetchAll();
 
     $assignUid = $db->prepare('UPDATE cards SET relay_uid = :u WHERE id = :id');