Refine Codex issue digest summaries

[etraut-openai]

Why

The codex-issue-digest skill was producing more detail than the daily digest needed, and broad all-area digests could miss active issues. In particular, issue #16088 had substantial recent comments and reactions but did not appear in the weekly all-areas output because GitHub search was using default relevance ranking and the collector could exhaust its candidate cap before later search queries got a fair sample.

That made the digest look quieter than the underlying user activity and made threshold tuning misleading.

What changed

• Make the digest summary headline-first and summary-only by default.
• Add an explicit opt-in flow for ## Details, so the issue table is shown only when requested or when the prompt asks for details upfront.
• Update the collector to request GitHub issue search results with sort=updated and order=desc.
• Apply the search candidate cap per query instead of globally across all queries.
• Bump the collector script version to 3.
• Add tests that cover updated sorting and per-query candidate limits.

Verification

• pytest .codex/skills/codex-issue-digest/scripts/test_collect_issue_digest.py
• ruff check .codex/skills/codex-issue-digest/scripts/collect_issue_digest.py .codex/skills/codex-issue-digest/scripts/test_collect_issue_digest.py
• git diff --check
• Reran the all-areas weekly collector and confirmed Starting a thread in a project without .codex leaves behind an empty .codex file #16088 is now included with 55 interactions.