Build an approval-gated production release pipeline

[kelvinkipruto]

Parent

#572

What to build

Create an approval-gated production release flow that builds once, promotes the exact verified image, runs migrations once before traffic switches, exposes bounded liveness/readiness checks, and supports a rehearsed rollback without requiring a live database to construct an image.

Acceptance criteria

• Production artifact creation does not require a reachable application database.
• CI produces an immutable image identified by digest and staging/production promote that same digest.
• Production deployment requires an approved GitHub environment or equivalent human approval.
• Migrations run as a single-instance observable release step, never concurrently in every replica.
• Migration failure prevents traffic switching and has documented forward-fix/rollback handling.
• Separate bounded liveness and readiness endpoints are wired into Docker/Dokku probes.
• Readiness checks MongoDB and Tika when they are required to serve traffic.
• Image rollback and database restore procedures are documented and successfully rehearsed.

Blocked by

• Create isolated tests and mandatory CI verification #578