v2.18.4 — kg_RRF_FUSE empty query_text fix

v2.18.4 (2026-09-07)

Spec hygiene: tasks.md sync, integration test fixes, embedding dimension

• Spec 039 (temporal Cypher): all 52 tasks marked [X]; spec status updated to
  Complete — 21 unit + 9 E2E tests pass at v2.18.4.
• Spec 040 (SQL table bridge): 52 tasks marked [X]; T034 (mixed mapped+native
  multi-hop) and T036-T044 (attach_embeddings E2E) remain [ ] — T034 requires
  translator work, T036-T044 require an embedding model.
• Spec 041 (embed-nodes): tasks.md created; unit and integration tests documented;
  vector recall E2E deferred pending real embedding model.
• Integration conftest: engine fixture now uses embedding_dimension=768 matching
  the container default — fixes test_store_embedding_and_knn IRIS vector dimension
  mismatch (SQLCODE field-validation failure).
• Temporal index integration tests: PurgeResult.deleted attribute used consistently
  throughout test_temporal_index_gaps_e2e.py — fixes two assertions that compared
  PurgeResult object directly to int.