RFD 3202: Weekly release train cadence

[lowlydba]

Ad-hoc releases are creating planning churn for maintainers and reviewers, especially when late changes arrive without clear cutoffs. This discussion proposes a weekly release train with a Thursday merge cutoff, Friday stabilization, and Monday rollback checkpoint based on production metrics. Teams can still ship urgent fixes, but only under a documented fast-track policy with approver rotation. We need feedback on whether this cadence conflicts with partner timelines, and whether the branch policy should include an automatic freeze label after cutoff to reduce accidental late merges.