feat(commands): add /seo-auditor — 7-phase SEO audit pipeline for documentation

- 7 phases: discovery → meta tags → content quality → keywords → links → sitemap → report
- Integrates 8 marketing-skill scripts: seo_checker, content_scorer,
  humanizer_scorer, headline_scorer, seo_optimizer, sitemap_analyzer,
  schema_validator, topic_cluster_mapper
- References 6 SEO knowledge bases for audit framework, AI search,
  content optimization, URL design, internal linking, AI detection
- Auto-fixes: generic titles, missing descriptions, broken links, orphan pages
- Preserves high-ranking pages — only fixes critical issues on those
- Registered in both commands/ (distributable) and .claude/commands/ (local)

Also: sync all doc counts — 28 plugins, 26 eng-core skills, 21 commands

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/plugins/index.md

@@ -1,13 +1,13 @@
 ---
 title: "Agent Plugin Marketplace — Codex & OpenClaw Plugins"
-description: "21 installable agent plugins for Claude Code, Codex CLI, Gemini CLI, and OpenClaw. One-command install for engineering, marketing, product, compliance, and finance skill bundles."
+description: "28 installable agent plugins for Claude Code, Codex CLI, Gemini CLI, and OpenClaw. One-command install for engineering, marketing, product, compliance, and finance skill bundles."
 ---
 
 <div class="skills-hero" markdown>
 
 # Plugins & Marketplace
 
-**19 installable plugins** — domain bundles and standalone packages distributed via Claude Code plugin registry and ClawHub.
+**28 installable plugins** — domain bundles and standalone packages distributed via Claude Code plugin registry and ClawHub.
 
 <p class="skills-hero-sub">Install entire skill domains or individual tools with a single command. Compatible with Claude Code, OpenAI Codex, Gemini CLI, and OpenClaw.</p>
 
@@ -19,7 +19,7 @@ description: "21 installable agent plugins for Claude Code, Codex CLI, Gemini CL
 
 <div class="grid cards" markdown>
 
--   :material-puzzle-outline:{ .lg .middle } **19 Plugins**
+-   :material-puzzle-outline:{ .lg .middle } **28 Plugins**
 
     ---
 
@@ -90,7 +90,7 @@ description: "21 installable agent plugins for Claude Code, Codex CLI, Gemini CL
 ```mermaid
 graph TB
     subgraph Registry["Plugin Registry"]
-        MP["marketplace.json<br/>19 plugins"]
+        MP["marketplace.json<br/>28 plugins"]
     end
 
     subgraph Bundles["Domain Bundles (9)"]