chore: close bot-opened issues when resolved

[prql-bot]

Summary

Adds an "Issue management" section to .claude/skills/running-tend/SKILL.md telling the bot to close its own resolved issues instead of leaving them open for a maintainer.

Evidence

• 2026-04-16, issue Nightly tests failed #5802 — nightly opened "Nightly tests failed", fix PRs ci: pin zig to 0.15.2 #5801 + ci: update minimal-zig example to Zig 0.16 API #5803 merged, main CI went green. Bot commented "Leaving open for a maintainer to close". @max-sixty pushed back (comment): "@prql-bot you should close these when things pass", and then "presumably we need to add this to the tend skill?".
• 2026-04-19, issue tend-review CI monitor polls --required, misses in-flight tests failures on opened PRs #5809 — the nightly noted "tend-review CI monitor polls --required, misses in-flight tests failures on opened PRs #5809 is already addressed by the bundled tend review skill's current statusCheckRollup-based polling — left for maintainer to close". Same pattern recurred.

Why this is in running-tend, not upstream tend

The parent nightly/triage/running-in-ci skills deliberately defer issue-closing authorization to the adopter-repo overlay (the "Helping vs. directing" rule). This repo welcomes bot-initiated housekeeping on bot-authored issues, so the authorization belongs here.

Test plan

• On next nightly, if a bot-opened issue is resolved, the bot closes it with a "Resolved by #NNNN" comment instead of deferring to a maintainer.

Generated by tend-review-runs run 24624548956.