[2.29.0] Add schema-drift-detector agent

- New agent: schema-drift-detector for catching unrelated schema.rb changes in PRs
- Compares schema.rb diff against migrations in the PR
- Detects columns, indexes, tables from other branches
- Provides clear fix instructions
- Essential pre-merge check for database changes

Also updates component counts in README (were outdated)

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

plugins/compound-engineering/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "compound-engineering",
-  "version": "2.28.0",
-  "description": "AI-powered development tools. 28 agents, 24 commands, 15 skills, 1 MCP server for code review, research, design, and workflow automation.",
+  "version": "2.29.0",
+  "description": "AI-powered development tools. 29 agents, 24 commands, 16 skills, 1 MCP server for code review, research, design, and workflow automation.",
   "author": {
     "name": "Kieran Klaassen",
     "email": "kieran@every.to",