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

docs/testing.md

@@ -18,6 +18,7 @@ Live in `tests/`. Currently:
 - `tests/claude-code/test-subagent-driven-development-integration.sh` — extended SDD integration with token analysis (drill covers the YAGNI subset; bash adds commit-count, Claude Code task-tracking, and token telemetry assertions).
 - `tests/claude-code/test-worktree-native-preference.sh` — RED-GREEN-REFACTOR validation for worktree skill (drill covers the PRESSURE phase; bash also covers RED/GREEN baselines).
 - `tests/explicit-skill-requests/` — Haiku-specific, multi-turn, and skill-name-prompted tests not covered by drill.
+- `tests/diagnosing-superpowers/test-skill-structure.sh` — structural checks for the diagnosing-superpowers skill (frontmatter, referenced files, leak scan, word budget); behavior-scenario eval records are kept by the maintainer outside the repo.
 
 Run plugin tests via the relevant directory's `run-*.sh` or `npm test`.