chore: remove new-pr label and 24 hour rule

[MarshallOfSound]

Removes the new-pr 🌱 label and everything that existed to manage it (24 hour rule handler, its cron, exclusion lists, tests, fixtures, README section).

API review used that label as its minimum open time gate, so that gate is now time based instead. checkPRReadyForMerge compares against the same ready time the check title already shows ("ready on "): opened / last marked ready for review + 7 days.

Things that behave differently:

• api-review/skip-delay ⏰ now actually skips the delay. Previously it only changed the date in the check title and the real bypass was fast-track / backport removing new-pr.
• The 5 minute cron lives in setupAPIReviewStateManagement now and only looks at open PRs that have an api-review/* label.
• The old cron paginated from page = 0 which GitHub treats as page 1, so the first 100 PRs were processed twice per run. Switched to octokit.paginate.

The new-pr 🌱 label itself will need deleting from electron/electron by hand after this deploys.

[nmggithub]

Astra tells me of this one correctness issue:

• [P2] Revoke existing approval when the delay applies again — src/api-review-state.ts, lines 411–418. If a young PR is approved using api-review/skip-delay and that label is subsequently removed, this early return preserves api-review/approved and the successful check until day seven. It also ignores subsequent API declines or change requests during that period. Reset premature approval to requested, and allow negative review outcomes to take effect. I reproduced the stale approval with a one-day-old PR and a subsequent decline.

this is completely unrelated to the act of removing the new-pr feature and exists before this change. dismissing review