docs(plugin-eval): add CLAUDE.md, full evaluation framework docs, and README updates

- Create CLAUDE.md with project conventions and PluginEval quick reference
- Add docs/plugin-eval.md with complete framework documentation (layers,
  dimensions, scoring, anti-patterns, statistical methods, project structure)
- Add PluginEval section to main README under What's New
- Expand plugin-eval/README.md with quick start and command table

plugins/plugin-eval/README.md

@@ -1,3 +1,38 @@
 # plugin-eval
 
 Three-layer quality evaluation framework for Claude Code plugins.
+
+## Quick Start
+
+```bash
+cd plugins/plugin-eval
+uv sync
+
+# Evaluate a skill (static only, instant)
+uv run plugin-eval score path/to/skill --depth quick
+
+# Evaluate with LLM judge (~30s)
+uv run plugin-eval score path/to/skill --depth standard
+
+# Full certification (all layers, ~5 min)
+uv run plugin-eval certify path/to/skill
+```
+
+## Layers
+
+1. **Static Analysis** — Structural checks, anti-pattern detection. Instant, free.
+2. **LLM Judge** — Semantic evaluation (triggering, orchestration, output, scope). ~30s, 4 calls.
+3. **Monte Carlo** — Statistical reliability via 50–100 simulated runs. ~2–5 min.
+
+## Commands
+
+| CLI                   | Claude Code | Description                   |
+| --------------------- | ----------- | ----------------------------- |
+| `plugin-eval score`   | `/eval`     | Score a plugin or skill       |
+| `plugin-eval certify` | `/certify`  | Full certification with badge |
+| `plugin-eval compare` | `/compare`  | Head-to-head comparison       |
+| `plugin-eval init`    | —           | Build corpus for Elo ranking  |
+
+## Documentation
+
+See **[docs/plugin-eval.md](../../docs/plugin-eval.md)** for the full reference: layers, dimensions, scoring formula, anti-patterns, statistical methods, and project structure.