ci: merge issue triage and reproduction into one intake bot; add triage-issues skill

One issue now gets one comment instead of two posted minutes apart
(the old triage bot asked questions its reproduce sibling then answered
itself). The combined issue-intake agent, driven by an audit of recent
bot output:

- duplicate check before anything else — duplicates are closed, not
  reproduced (the duplicate label had zero uses across 1,353 issues
  while the bot found duplicates in prose)
- reproduction artifacts live in a collapsed block inside the comment;
  the reproduce/issue-N branch convention is retired (382 stale branches
  removed from origin)
- reproducible:true renamed to root-cause:found — it asserts a traced
  mechanism, not reporter-confirmed causation; confirmed:reporter is the
  human-set complement
- the bot no longer sets priority (maintainer-only flag), announces its
  labels, opens with flattery, or interrogates feature reporters about
  design decisions
- comment opens with a For-the-maintainer line (fix-ready /
  needs-reporter / duplicate / likely-fixed / feature)
- label taxonomy cut from 65 to ~26: api:*, reproduction-steps:*,
  priority:medium/low, 13 near-zero-use area labels, ios/android
  platforms, and orphans removed
- runs on zai-coding-plan/glm-5.3-flash via ZHIPU_API_KEY
- new triage-issues skill mirrors the PR triage pipeline: mechanical
  sweep, verdict fan-out, approved batch actions, fix backlog

AGENTS.md

@@ -104,6 +104,7 @@ process violation.
 | Creating or editing skills, `AGENTS.md`, or docs reached through agent instructions/context pointers | `writing-for-agents` |
 | Reviewing a single pull request or drafting a PR verdict/close/review comment | `pr-review` |
 | Triaging, cleaning up, or batch-processing the open PR queue | `triage-prs` |
+| Triaging, cleaning up, or batch-processing the issue backlog | `triage-issues` |
 
 Pure code-reading or explanation does not require implementation skills unless needed to interpret a specialized subsystem.