[2.16.0] Consolidate DHH styles and add /feature-video command

- Merge dhh-ruby-style into dhh-rails-style for comprehensive Rails conventions
- Add testing.md reference covering Rails testing patterns
- Add /feature-video command for recording PR demo videos
- Update docs and component counts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -11,8 +11,8 @@
   "plugins": [
     {
       "name": "compound-engineering",
-      "description": "AI-powered development tools that get smarter with every use. Make each unit of engineering work easier than the last. Includes 27 specialized agents, 19 commands, and 13 skills.",
-      "version": "2.18.0",
+      "description": "AI-powered development tools that get smarter with every use. Make each unit of engineering work easier than the last. Includes 27 specialized agents, 20 commands, and 12 skills.",
+      "version": "2.20.0",
       "author": {
         "name": "Kieran Klaassen",
         "url": "https://github.com/kieranklaassen",