New endpoint GET /v1/brain/search?q=<query>&org=<>&project=<>&limit=<N>
that full-text-searches brain_memories via Elasticsearch using
BrainService::elasticSearch(). Separate from /v1/brain/recall (which is
vector/semantic via Qdrant) — this one is keyword/lexical.
Sits under the existing brain.read-auth middleware group.
Pest coverage (Http::fake for ES): Good (matches), Bad (invalid limit),
Ugly (empty query + filters).
Co-authored-by: Codex <noreply@openai.com>
Closes tasks.lthn.sh/view.php?id=64
