Phase 8.3 — Secret management rollout

Deploying proper secret management and retrofitting existing deployments onto it.

Secrets are currently spread across pipeline variables and per-application configuration. This subphase introduces a managed approach and migrates existing applications to it, so credentials are stored, rotated and audited in one place instead of being duplicated per repository.

Planned — renumbered from Phase 6.5, now part of Phase 8 — Platform maturity.