v2.7.0

release: v2.7.0 — 90% test coverage

43 new unit test files; 7,000+ assertions across translator, parser,
query engine, snapshot, schema, admin, bulk loader, embeddings, vector,
cypher API, GQL, fusion, embedded, RDF/SHACL/prov.

Two translator bug fixes found during coverage work:
- Add missing _format_tz_for_iso helper (dead-code in
  _build_temporal_from_variable_map — never defined)
- arg.name → arg.function_name for FunctionCall nodes in
  vector search argument resolution (line 776)

Coverage: 74% (v2.6.0) → 90% (21,058 statements)