feat: add role management and usage tracking modules

- Implemented role parsing and loading functionality in roles.js, allowing for structured role definitions with metadata.
- Added tests for role management to ensure correct parsing and loading of roles.
- Created usage.js to track API usage metrics, including token counts and rate limits.
- Developed tests for usage tracking to validate functionality and edge cases.
- Enhanced overall code structure and documentation for clarity and maintainability.

app/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "ai-code-review",
+  "version": "1.0.0",
+  "type": "module",
+  "scripts": {
+    "test": "node --test *.test.js"
+  },
+  "dependencies": {
+    "axios": "^1.6.7",
+    "js-yaml": "^4.1.0",
+    "openai": "^4.28.0"
+  }
+}