fix(scripts): propagate top-level failures

[RerankerGuo]

Summary

• return a failing process status when either duplicate-maintenance script rejects at the top level
• keep logging the original error while allowing pending output to flush

Problem

Both scripts used .catch(console.error). That reports startup and API failures but resolves the rejection, so the Bun process exits successfully. In CI, a missing token or top-level GitHub API failure can therefore look like a successful maintenance run.

Verification

• GITHUB_TOKEN= node scripts/auto-close-duplicates.ts returns 1
• GITHUB_TOKEN= node scripts/backfill-duplicate-comments.ts returns 1
• both scripts return 0 with a stubbed successful GitHub API response containing an empty result set
• git diff --check

Scope

Per-issue failures in auto-close-duplicates.ts remain best-effort so one issue does not stop the batch. This only changes unhandled top-level failures.