fix: use fetched embedding property in vector cypher retriever

[liuzemei]

Summary

• use the fetched _embedding_node_property for VectorCypherRetriever filtered fallback queries
• add a regression test for the procedure fallback path with metadata filters

Fixes #540

Tests

• uv run pytest tests/unit/retrievers/test_vector.py::TestVectorCypherRetrieverSearchClausePath::test_filtered_fallback_uses_fetched_embedding_property -q
• uv run pytest tests/unit/retrievers/test_vector.py -q
• uv run pytest tests/unit/retrievers/test_base.py tests/unit/retrievers/test_hybrid.py tests/unit/retrievers/test_retriever_parameter_inference.py tests/unit/retrievers/test_text2cypher.py tests/unit/retrievers/test_tools_retriever.py tests/unit/retrievers/test_vector.py -q
• uv run ruff format --check src/neo4j_graphrag/retrievers/vector.py tests/unit/retrievers/test_vector.py
• uv run ruff check src/neo4j_graphrag/retrievers/vector.py tests/unit/retrievers/test_vector.py
• git diff --check