fix(homecore-assist): exact in-memory cosine k-NN, drop fragile :memory: HNSW

The semantic recognizer built a ruvector-core VectorDB at ":memory:"; under
full-workspace feature unification the file-storage backend is enabled and
":memory:" is an invalid Windows filename (os error 123), panicking via
.expect(). Replace the external index with an exact in-memory cosine k-NN over
the enrolled exemplars (embeddings are L2-normalised, so cosine = dot product).
For HOMECORE's small intent vocabularies this is faster, fully deterministic,
and removes the storage backend + cross-crate feature coupling entirely.
ruvector-core dropped from the crate (only used here). Workspace 3122 passed/0 failed.

Co-Authored-By: claude-flow <ruv@ruv.net>

v2/Cargo.lock

@@ -10972,6 +10972,7 @@ dependencies = [
  "ruvector-temporal-tensor",
  "serde",
  "serde_json",
+ "serialport",
  "thiserror 2.0.18",
  "tokio",
  "tokio-test",