Add code-simplifier plugin

Adds a code simplification agent that:
- Simplifies and refines code for clarity and maintainability
- Preserves all functionality while improving code structure
- Follows project-specific best practices from CLAUDE.md
- Focuses on recently modified code unless instructed otherwise

plugins/code-simplifier/.claude-plugin/plugin.json

@@ -0,0 +1,9 @@
+{
+  "name": "code-simplifier",
+  "version": "1.0.0",
+  "description": "Agent that simplifies and refines code for clarity, consistency, and maintainability while preserving functionality",
+  "author": {
+    "name": "Anthropic",
+    "email": "support@anthropic.com"
+  }
+}