feat: add diagnosing-superpowers skill

Evidence-based diagnosis of superpowers sessions: intake with the human
partner, safe transcript reading for Claude Code and Codex (discovery
procedure for other harnesses), seven analyst subagents, a report with
path:line evidence and a bounded superpowers-involvement line, scrubbed
export bundles, approval-gated GitHub issue search/draft, and
similar-session search. Includes spec, plan, structure test, and README
and docs index lines.

Developed RED-GREEN-REFACTOR per writing-skills: 46 scored scenario runs
across five SKILL.md versions, all twelve scenarios clean against the
final version, micro-tests control 5/5 to skill 0/5 on both
baseline-failing prohibitions, and one end-to-end run. Eval records are
kept by the maintainer outside the repo.

Claude-Session: https://claude.ai/code/session_01DyaGKhTXvHNs2JgPhDktz7

skills/diagnosing-superpowers/templates/issue.md

@@ -0,0 +1,49 @@
+- [x] I searched existing issues and this is not a duplicate (searched: <query terms>; closest: <#n title, or "none">)
+
+## Environment (required)
+
+| Field | Value |
+|-------|-------|
+| Superpowers version | <version> (<sha or "not a checkout">) |
+| Harness (Claude Code, Cursor, etc.) | <harness> |
+| Harness version | <version> |
+| Your model + version | <model ids seen> |
+| All plugins installed | <list> |
+| OS + shell | <os version>, <shell> |
+
+## Is this a Superpowers issue or a platform issue?
+
+- [ ] I confirmed this issue does not occur without Superpowers installed
+
+Not reproduced without superpowers. Evidence for involvement is below;
+the reporter has not established cause.
+
+## What happened?
+
+<Problem statement, then the triage verdict, with `path:line` citations
+rewritten as `transcript line <n>`.>
+
+## Steps to reproduce
+
+1. <first human prompt, scrubbed>
+2. <the turns leading to the problem, one line each>
+3. <the observable>
+
+## Expected behavior
+
+<from the problem statement>
+
+## Actual behavior
+
+<from the triage verdict>
+
+## Debug log or conversation transcript
+
+Session id(s): <ids>. A scrubbed bundle (redaction level: <level>) is
+attached to this issue by the reporter, or available on request.
+Superpowers involvement per the diagnosis report: <possible | likely>, with
+evidence at <transcript lines>. This report does not propose a fix.
+
+---
+Filed with the `diagnosing-superpowers` skill. Model, harness, harness
+version, and installed plugins are listed above.