refactor(notes): remove legacy whole-document saves; all block changes go through sync

Phase 5 of the collaboration plan:
- Remove PATCH /documents/{id}/blocks, PatchDocumentBlocks, the
  DOC_BLOCKS_PATCHED event and its types, FlushDocumentState and
  LoadDocumentState. PUT /documents/{id} rejects blocks (400) and only
  changes title, icon, folder and pin; editors may now change title/icon.
- The to-do overview ticks via a single operation on /docs/{id}/sync
  (new skipLog flag). Task links set the block tick with a targeted
  operation and notify open editors; creating a linked task needs edit
  rights.
- Keep the three share tables: DocRole already decides centrally, and
  rewriting the visibility queries would only add risk (documented in plan).
- Tests adapted to the new paths; share e2e test now also ticks a to-do in
  the overview.

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

frontend/src/features/workspace/WorkspaceView.tsx

@@ -49,6 +49,7 @@ import {
   RealtimeTransport,
 } from '../../lib/api';
 import { UnifiedShareModal } from '../../components/UnifiedShareModal';
+import { sendDocOps } from '../../lib/docSync/oneoff';
 import { useMobileActions } from '../../context/MobileActionContext';
 import { DocumentEditor, DocSaveStatus } from './DocumentEditor';
 
@@ -789,9 +790,8 @@ export const WorkspaceView: React.FC<WorkspaceViewProps> = ({
       prev.map((d) => (d.id === doc.id ? { ...d, blocks: updatedBlocks } : d))
     );
     try {
-      await api.patchDocumentBlocks(doc.id, {
-        upserted: [{ id: blockId, checked: !currentChecked, type: 'todo', content: '' }],
-      });
+      const [result] = await sendDocOps(doc.id, [{ kind: 'set_props', blockId, patch: { checked: !currentChecked } }]);
+      if (result?.status !== 'applied') loadWorkspaceData();
     } catch {
       loadWorkspaceData();
     }