Next-gen DevOps Center: promotion to RELEASE consistently fails with "SFAP API call failed" during Promotion Completed step

# Title
Next-gen DevOps Center: promotion to RELEASE consistently fails with "SFAP API call failed" during Promotion Completed step

## Summary
Promoting work items from VALIDATION to RELEASE in a next-gen DevOps Center pipeline (not the managed package — confirmed "Enable DevOps Center" is on, "Enable DevOps Center Managed Package" is off) fails reliably at the final "Promotion Completed" activity, after every "Promotion Work Item" validation step has already succeeded. The deploy itself is not the problem — deploying the same source directly via `sf project deploy start` to the same target org succeeds cleanly every time.

## Environment
- Control org: orgfarm-99e650705e-dev-ed.develop.lightning.force.com (Org ID 00Dfj00000avkat)
- Pipeline: Grand Bazaar Companion Pipeline
- Release Environment: GBC RELEASE (gbcrelease-dev-ed.develop.my.salesforce.com)
- Product: next-gen DevOps Center (native), not the managed package

## Errors observed (same failure point, different underlying messages across attempts)
- `Callout failed : SFAP API call failed with status code: 400, Response: {errors=[{message=fetch failed}]}`
- `Callout failed : SFAP API call failed with status code: 400, Response: {errors=[{message=Failed to get valid user info after max retries}]}`
- One attempt also hit: `SSL connection failed during named credential callout: Certificate for doesn't match any of the subject alternative names: [...]`

All at Activity Type "Promotion Completed", Pipeline Stage "RELEASE". DevOps Activity Log records: DOAL-000000454, DOAL-000000465, DOAL-000000476, DOAL-000000487.

## What we've ruled out
- Not a metadata/deployability problem: the identical source deploys successfully via Salesforce CLI directly to the same target org.
- Not tied to the pipeline's "Agentforce Vibes Org" setting: removing that association entirely did not change the failure mode (same SFAP error class recurred).
- Not user-specific: reproduced identically under two different System Administrator users.
- Not source-control related: this is a separate, distinct issue from an unrelated `ALMDevOpsCenterHub-PerUserPrincipal` deployment error we hit and resolved ourselves (a bad permission-set reference committed to our own repo) — that fix is confirmed unrelated to this SFAP failure, which persists after it.

## Impact
Promotion from VALIDATION to RELEASE is unreliable/blocked via the DevOps Center UI. We are currently working around this by deploying directly via Salesforce CLI from our validated integration branch, bypassing DevOps Center's promotion mechanism for the final RELEASE step.

## Request
Please investigate why the "Promotion Completed" step's SFAP API callout is failing for this pipeline/org, and what's needed to make VALIDATION→RELEASE promotion reliable again in next-gen DevOps Center.

Start by reproducing VALIDATION→RELEASE promotion and reviewing DevOps Activity Log records DOAL-000000454, DOAL-000000465, DOAL-000000476, and DOAL-000000487 at the Promotion Completed step. Compare the failing DevOps Center flow with the successful `sf project deploy start` deployment and the reported SFAP, user-info, and certificate errors. Done means promotion completes reliably for the stated pipeline and target org.

Written by the indexing model from the issue text.