feat(tasks): linked tasks sync title and subtasks with their note in both directions

Subtasks of a task linked to a note checkbox are tied 1:1 to checkboxes of that note
(subtasks[].blockId), wherever they are moved. ReconcileDocTaskLinks now carries tick, title and
subtasks from the note to the task and adopts new checkboxes directly under the task;
SyncTaskToDoc carries tick, title and subtasks to the note and adds checkboxes for new subtasks.
Deleting is not mirrored. Deepening a task ties its subtasks right away; saves without links keep
the server's links. The sync response reports taskLinks/subtaskLinks; the editor shows an
"Unteraufgabe" badge. v0.36.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/handlers_documents.go

@@ -205,6 +205,12 @@ func (s *Server) handleCreateEnhancedTask(w http.ResponseWriter, r *http.Request
 		writeError(w, http.StatusBadRequest, err.Error())
 		return
 	}
+	// Checkboxes already right under it become its subtasks (task_doc_sync.go)
+	if len(s.store.ReconcileDocTaskLinks(docID)) > 0 {
+		if fresh, err := s.store.GetThoughtByIDUnchecked(thought.ID); err == nil && fresh != nil {
+			thought = fresh
+		}
+	}
 	_, head, _ := s.store.GetDocOpsSince(docID, 0, 0)
 	s.notifyDocChanged(docID, head)