Nightly quality probe silently skips on compiled binary installs while reporting as enabled

Summary

autopilot.nightly_quality_probe.enabled is true on our brain and the cap is configured, but the probe never runs: it needs test/fixtures/longmemeval-nightly.jsonl from the package, and a compiled single-file binary install has no such path, so the probe skips quietly.

Impact

For binary installs — the attested release asset, which is the recommended supply-chain-safe way to run gbrain — there is no automated retrieval-quality regression at all, and the configuration says otherwise. Operators discover it only by auditing why the probe never appears in the logs or in chat_usage_log.

Expected

Either embed the fixture in the binary, or make the skip visible (a doctor check / autopilot --status line naming "probe unavailable on this install method") so a configured-but-inert control does not read as an active one.

Environment

0.50.5.0 / 0.51.0.0, darwin-arm64 release asset, Postgres brain.