Add code-review plugin with automated PR review workflow

Add new code-review plugin that provides automated pull request reviews using multiple specialized agents with confidence-based scoring to filter false positives.

Key features:
- Multiple parallel agents for independent auditing (CLAUDE.md compliance, bug detection, historical context)
- Confidence-based scoring (0-100) with 80+ threshold to filter false positives
- Automatic skipping of closed, draft, or already-reviewed PRs
- Links directly to code with full SHA and line ranges

Updates:
- Add code-review plugin directory with command and README
- Update plugins/README.md to document the new plugin

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

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

plugins/README.md

@@ -32,6 +32,16 @@ Simplifies common git operations with streamlined commands for committing, pushi
   - `/clean_gone` - Clean up stale local branches marked as [gone]
 - **Use case**: Faster git workflows with less context switching
 
+### [code-review](./code-review/)
+
+**Automated Pull Request Code Review Plugin**
+
+Provides automated code review for pull requests using multiple specialized agents with confidence-based scoring to filter false positives.
+
+- **Command**:
+  - `/code-review` - Automated PR review workflow
+- **Use case**: Automated code review on pull requests with high-confidence issue detection (threshold ≥80)
+
 ### [feature-dev](./feature-dev/)
 
 **Comprehensive Feature Development Workflow Plugin**