Milvus supports multiple databases, but the sidebar only ever showed
collections under the hardcoded "default" database. The backend returned
["default"] for every vector store and the frontend loaded collections
for a single database and flattened them under the connection node.
- Backend (vector_driver): add list_databases() that calls Milvus
/v2/vectordb/databases/list (falling back to "default" for older Milvus
and for non-Milvus vector stores), and thread a database parameter
through find_documents() instead of hardcoding "default".
- document_ops: list_databases_core delegates VectorDb to list_databases();
find_documents_core forwards the selected database.
- Frontend: add a "vector-database" tree node type. For Milvus, connections
expand into database nodes, which expand into their own collections.
Collection node ids are namespaced by database to avoid collisions
across databases, and the collection id is stored in meta so activation
no longer parses the node id.
Fixes#2693
Co-authored-by: 朱豪豪 <zhu.hh.sz@belle.com.cn>
hhzorg