Align the claim timeout and PR entry flow with the Season 4 CLI bonus rules #554

The Season 4 hackathon rules and this repository's bots disagree in two places:

1. Claim timeout. The rules promise a warning at 48 hours and a release at 72 hours. claim-ttl.yml warns at 72 and releases at 96.
2. Bonus entry. The rules say a PR enters the CLI Improvement Bonus by ticking a checkbox in the PR template, and that a bot confirms the entry in a comment. The template has no such checkbox, and no workflow confirms entries.

Fixes:

• ci(oss): warn idle claims at 48 hours and release them at 72 #552 moves the claim sweep to 48/72.
• ci(oss): confirm Season 4 CLI bonus entries from the PR template checkbox #553 adds the template checkbox and the entry-confirmation bot.