create_bank_hnsw_indexes() hardcoded USING hnsw regardless of the configured
vector extension, causing "column cannot have more than 2000 dimensions for
hnsw index" when using pgvectorscale or vchord with high-dimensional embeddings.
Now reads get_config().vector_extension and uses the appropriate index type:
- pgvector → USING hnsw
- pgvectorscale → USING diskann
- vchord → USING vchordrq
Closes#738
6488c9bc77