[refactor] cut-criteria multi-milestone support

[trilamsr]

PR #374 ships executable cut-criteria but docs/cut-criteria.yaml + scripts/cut-criteria-{status,render}.sh hardcode v1-rc1.

Asks:

• Add milestone: field per criterion (v1-rc1 / v1-ga / v1.1 / etc).
• Parameterize render output: make cut-criteria-render MILESTONE=v1-rc1 → docs/v1-rc1-cut-criteria.md.
• Multi-milestone status overview command: make cut-criteria-status-all.

When: before v1-rc2 cut. Currently fine for v1-rc1 ship.

Tracked from: review of PR #374 + user feedback on roadmap reusability.