feat: continuous staging deploys with Tue-Thu freeze for prod promotion

[Evrard-Nil]

Summary

• Build workflow (build.yml): every push to main now also tags :staging, enabling continuous deployment to the staging environment
• Staging freeze: on Tuesday and Wednesday (UTC), the :staging tag is not updated — the staging environment stays stable for prod-candidate testing
• Promote workflow (promote.yml): simplified to a single Thursday cron job that promotes the frozen :staging → :prod

Weekly cadence

Mon:       commit → :latest + :staging  (CI to staging)
Tue 00:00: staging freeze begins        (last Mon commit is the candidate)
Tue–Wed:   commit → :latest only        (staging untouched, testing the candidate)
Thu 00:00: :staging → :prod             (promote tested candidate)
Thu–Sun:   commit → :latest + :staging  (CI resumes)

Test plan

• Verify build workflow tags :staging on a main push outside the freeze window
• Verify build workflow skips :staging tag on Tuesday/Wednesday (UTC)
• Verify Thursday cron promotes :staging → :prod
• Verify manual workflow_dispatch with prod target works

🤖 Generated with Claude Code

[gemini-code-assist]

Note

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[PierreLeGuen]

Should it also cut the release?

[PierreLeGuen]

LGTM. Clean CI/CD workflow — staging freeze on Tue-Wed with Thursday promotion to prod makes sense. All checks pass.