Remove the Brain search reranker

[mrubens]

Why

While evaluating whether the reranker earns its keep, we found it has never actually run:

1. gbrain's init (writeNewInstallRerankerDefault) writes search.reranker.enabled=false at Brain creation for installs keyed the way ours are (no VOYAGE_API_KEY). Our entrypoint set the reranker model after init but never flipped enabled — its reranker: boot log line was cosmetic. Verified in the config table of our deployments.
2. Even force-enabled, openrouter:voyageai/rerank-2.5-lite is not on the OpenRouter recipe's strict rerank model allowlist (Cohere v3.5/4-fast/4-pro + one NVIDIA model), so every call throws pre-HTTP and the fail-open contract silently returns RRF order. Failures land only in an in-container audit JSONL.

A 72-query known-item A/B (gold page per query, reranker off vs force-enabled, config restored after) confirmed it: 0/72 result lists changed, and the pure hybrid-RRF baseline everyone has been using all along scores hit@1 68% / hit@5 90% / hit@20 97%, median gold rank 1.

So this PR makes reality the explicit contract instead of an accident. Search behavior is unchanged by construction; autocut already no-ops without rerank scores by design.

What

• entrypoint: replaces the reranker gateway wiring with an explicit gbrain config set search.reranker.enabled false — converges pre-existing brains and is immune to upstream mode-bundle default flips (one is planned for September).
• inference gateway: drops /v1/rerank from the Brain's allowed paths, the rerank upstream branch, and the OpenRouter-only guard; tests updated (rerank path now 403s like any unlisted path).
• compose bundles: stop passing GBRAIN_RERANKER_MODEL/R_BRAIN_RERANKER_MODEL/R_BRAIN_RERANK_UPSTREAM_URL, and the local-inference Infinity service no longer loads BAAI/bge-reranker-v2-m3 (several GB of RAM for a model nothing calls).
• env schema / example / docs: reranker variables and instructions removed; docs now state Memory retrieval is hybrid RRF with no cross-encoder stage.

If we ever want a real reranker, the path is an allowlisted model (e.g. openrouter:cohere/rerank-4-fast) or a local upstream — gated on an A/B showing it actually helps.

Testing

• @roomote/api: 1910 passed (brain-inference suite updated).
• @roomote/dev gbrain-image test, compose security contract validator, bash -n on the entrypoint: all pass.
• Prod compose resolves; the self-host compose fragment parse quirk under bare docker compose config is pre-existing and unchanged.

[roomote-community]

No code issues found. See task

• Remove stale reranker variables and operator guidance from the Coolify, Railway, and Render deployment templates.

_{Reviewed 64c557b}