fix(eve): show vercel login device URL in dev TUI /login prompt

[wjx]

Description

In the dev TUI, /login runs vercel login, which prints a device-authorization URL on stderr. When running locally this isn't noticed because a browser opens automatically, but on a remote server no browser opens — and the URL was being suppressed by the open choice panel (which waits on "Complete the login in your browser"). With no visible URL, there was no way to finish login by hand.

This change keeps the streaming vercel login subprocess output (including the device URL) visible alongside the parked prompt's actions, instead of dropping it the way a single status line is. A preview field carries the recent output buffer onto the question panel, capped to the last few lines.

How did you test your changes?

• Added a regression unit test in packages/eve/src/cli/dev/tui/terminal-renderer.test.ts ("shows subprocess output (e.g. a login URL) while a choice panel is open") asserting the device URL survives in the panel even after a later output line.
• pnpm typecheck — passed
• pnpm lint — passed
• pnpm fmt — clean
• pnpm test (unit + integration) — passed (323 integration tests; new unit test passes)

PR Checklist

• I ran the relevant checks from CONTRIBUTING.md
• I added tests and documentation where relevant
• I added a changeset if this touches the published eve package
• DCO sign-off passes for every commit (git commit --signoff)

[vercel]

@wjx is attempting to deploy a commit to the Vercel Team on Vercel.

A member of the Team first needs to authorize it.