Friday-afternoon shipping window — opt-out next sprint

The "no deploys after 14:00 Friday" rule has been in place for two years. It catches a real class of weekend incidents, but it also burns Friday afternoons for teams that ship low-risk PRs.

Starting next sprint, the policy becomes opt-in per service:

• Default behaviour is unchanged — the deploy pipeline blocks production deploys after 14:00 local.
• A service can opt out by adding friday_afternoon_deploys: allowed to its service.yaml.
• Opting out requires the owning EM's signoff (the file enforces an EM-only CODEOWNER for that key).

Two reasons we're loosening it now: trunk-based CI catches regressions earlier than it did in 2024, and the on-call rotation has full APAC coverage so a Friday deploy isn't a EU-only burden.

If your team wants to opt out, the PR template is in runbooks/opt-out-friday.md.