test(task-61): lock graph store compat gaps

[earayu]

Summary

• Add cross-backend compat coverage for remove_relation_lineage_member dual-side rewrite: evidence_lineage and description_parts both drop the target document while unrelated relation evidence remains.
• Add missing-relation no-op coverage for relation lineage cleanup.
• Add list_entities stable pagination/sort coverage: deterministic name order across pages, label-filtered pagination, and limit/offset edge semantics.

Validation

• uv run --extra test pytest tests/integration/compat/test_lineage_graph_compat.py -q (local env has no compat DBs: 45 skipped)
• uv run --extra test pytest tests/unit_test/indexing/test_t1_2_graph.py -k "list_entities or remove_relation" -q (7 passed)
• uv run ruff check tests/integration/compat/test_lineage_graph_compat.py
• git diff --check

Scope

Task #61 P1-G1/G2 only. No P2 alias batching or production behavior changes.