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>

internal/storage/docsync_test.go

@@ -77,9 +77,7 @@ func TestLegacySaveRoundTripsThroughTheLog(t *testing.T) {
 
 	// Saving the same content again must not produce any log entries
 	head := headSeq(t, s, doc.ID)
-	if _, err := s.UpdateDocument(u.ID, doc.ID, nil, nil, nil, &initial, nil, nil); err != nil {
-		t.Fatal(err)
-	}
+	s.replaceDocBlocksInDB(doc.ID, u.ID, initial, "")
 	if h := headSeq(t, s, doc.ID); h != head {
 		t.Fatalf("unchanged save wrote %d log entries", h-head)
 	}
@@ -92,9 +90,7 @@ func TestLegacySaveRoundTripsThroughTheLog(t *testing.T) {
 		[3]interface{}{"c", 1, "Detail"},
 		[3]interface{}{"n", 2, "Neu"},
 	)
-	if _, err := s.UpdateDocument(u.ID, doc.ID, nil, nil, nil, &changed, nil, nil); err != nil {
-		t.Fatal(err)
-	}
+	s.replaceDocBlocksInDB(doc.ID, u.ID, changed, "")
 	got, _ = s.GetDocumentByID(u.ID, doc.ID)
 	sameOutline(t, got.Blocks, changed)