[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Also updates component counts in README (were outdated)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/README.md

@@ -6,16 +6,16 @@ AI-powered development tools that get smarter with every use. Make each unit of
 
 | Component | Count |
 |-----------|-------|
-| Agents | 27 |
-| Commands | 20 |
-| Skills | 14 |
+| Agents | 29 |
+| Commands | 24 |
+| Skills | 16 |
 | MCP Servers | 1 |
 
 ## Agents
 
 Agents are organized into categories for easier discovery.
 
-### Review (14)
+### Review (15)
 
 | Agent | Description |
 |-------|-------------|
@@ -26,21 +26,23 @@ Agents are organized into categories for easier discovery.
 | `data-migration-expert` | Validate ID mappings match production, check for swapped values |
 | `deployment-verification-agent` | Create Go/No-Go deployment checklists for risky data changes |
 | `dhh-rails-reviewer` | Rails review from DHH's perspective |
+| `julik-frontend-races-reviewer` | Review JavaScript/Stimulus code for race conditions |
 | `kieran-rails-reviewer` | Rails code review with strict conventions |
 | `kieran-python-reviewer` | Python code review with strict conventions |
 | `kieran-typescript-reviewer` | TypeScript code review with strict conventions |
 | `pattern-recognition-specialist` | Analyze code for patterns and anti-patterns |
 | `performance-oracle` | Performance analysis and optimization |
+| `schema-drift-detector` | Detect unrelated schema.rb changes in PRs |
 | `security-sentinel` | Security audits and vulnerability assessments |
-| `julik-frontend-races-reviewer` | Review JavaScript/Stimulus code for race conditions |
 
-### Research (4)
+### Research (5)
 
 | Agent | Description |
 |-------|-------------|
 | `best-practices-researcher` | Gather external best practices and examples |
 | `framework-docs-researcher` | Research framework documentation and best practices |
 | `git-history-analyzer` | Analyze git history and code evolution |
+| `learnings-researcher` | Search institutional learnings for relevant past solutions |
 | `repo-research-analyst` | Research repository structure and conventions |
 
 ### Design (3)