[Ticket]: Verify the live 5.1 deployment - prod device login and rollback procedure

### Type
Feature

### Summary
Promote 5.1.0 to prod and run the post-deploy verification.

### Intent
So the release is proven in the environment that matters, not only in CI.

### Source of truth (links)
- ADR-0023 (mandatory IdP surface)
- `docs/local-testing.md` (the same checks, run locally first)

### Current Behavior
Prod runs the pre-5.1 image; the new IdP surface is unavailable there.

### Expected Behavior
Prod serves the full IdP surface: discovery advertises introspection and the check-session iframe, and every advertised endpoint responds.

### Acceptance Criteria
- [ ] All pods healthy after sync
- [ ] `/.well-known/openid-configuration` lists `introspection_endpoint` and `check_session_iframe`
- [ ] Every advertised endpoint returns non-404 (the #473 failure mode was an advertised-but-unmounted route)
- [ ] A device-code login completes against prod
- [ ] Rollback procedure written down BEFORE promotion

### Out of Scope
New feature verification; this confirms parity plus the newly advertised routes.

### Technical Context
ADR-0023 mounts every IdP route unconditionally. The specific regression to check for is discovery advertising a route that 404s.

### Risks
A failed deploy on a Friday with no written rollback is the worst case. Write the rollback first.

### Test Plan
Run the post-deploy smoke script; capture output in this ticket as verification evidence.

### Verification evidence
- [ ] Test added and proven to fail before the change
- [ ] `just all-checks` green
- [ ] Every new or changed `src` file is <= 200 LoC

### Human accountable owner
@stephane-segning

### AI Usage Declaration
Ticket drafted with AI assistance from a verified repo audit.
Structure and estimates drafted with AI from a verified repository audit (file
line counts, config keys, and dependency state were read from the actual tree,
not assumed). A human owns intent, scope, and the release commitment.

### Human verification completed
- [ ] I can explain this work without referring to the AI-generated text
- [ ] Acceptance criteria are testable
- [ ] Source of truth is a real link, not boilerplate

Governance: https://adorsys-gis.github.io/ai-governance/

Start with ADR-0023 and docs/local-testing.md, then locate and run the post-deploy smoke script locally first. Write down the rollback procedure before promotion. Done means healthy pods, the required discovery entries, non-404 advertised endpoints, a completed device-code login, captured verification evidence, and green just all-checks.

Escrito por el modelo de indexación a partir del texto del issue.