Fix 4 bugs: SQL conflict handling, HTML escaping, backup cap, safe int cast

- sync_to_db: use ON CONFLICT for duplicate sequence numbers
- history_tree: html.escape() for Graphviz DOT labels
- tab_timeline_ng: cap history_tree_backup to 10 entries
- tab_batch_ng: add _safe_int() helper for VACE settings

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tab_timeline_ng.py

@@ -13,6 +13,7 @@ def _delete_nodes(htree, data, file_path, node_ids):
     if 'history_tree_backup' not in data:
         data['history_tree_backup'] = []
     data['history_tree_backup'].append(copy.deepcopy(htree.to_dict()))
+    data['history_tree_backup'] = data['history_tree_backup'][-10:]
     for nid in node_ids:
         htree.nodes.pop(nid, None)
     for b, tip in list(htree.branches.items()):