Vector queries over views at a stated revision (VV6) #328

Part of epic #305.

Problem. Queries can only search base-relation indexes; a view that reads an index is marked reads_untracked_state and refreshes on every commit (src/protocol/subscription/dependencies.rs:40-50).

Target. hnsw_nearest over an index on a view, resolved against the index state at the query's revision (at: or frontier); dependencies of index-reading views name the indexed relation or view instead of Everything; .why over vector rules reports the index epoch.

Acceptance. ?user(7,_,QV), hnsw_nearest("rec_idx", QV, 5, Id, D) at: r returns the same rows as the view's rows at r; a commit to an unrelated relation does not refresh an index-reading view (counter); proofs over vector rules pass why_tests.

Size S. Dependencies VV3, V9. Order slot 8.