The terminal's waves screen cuts a wave with `c` and a confirm: a draft pull listing every pull merged since the last wave, as the waves page does #7324

Intent: the owner tells the story of what shipped from the terminal, with no model called.

Done:

• [ ] On the waves screen (src/tui/screens/waves.ts), a repository admin presses c; the screen says how many pulls since the last wave would go into it and asks cut wave N? y/n.
• [ ] y calls cutWaveFor (src/actions/cut_wave.ts) and shows the draft pull's number; Enter opens it.
• [ ] Nothing merged since the last wave, an earlier wave that does not parse, or a viewer who is not an admin is refused in the action's words, and nothing is written.
• [ ] test/tui-waves.test.ts gains a case that cuts a wave and sees the pull, and one with nothing to cut.

Files: src/tui/screens/waves.ts, test/tui-waves.test.ts.