docs(auth): add RBAC explanation to requireRole middleware

Add JSDoc comment explaining Role-Based Access Control (RBAC) middleware
functionality for the requireRole() function.

Context: Safe documentation change from stress testing cleanup. Reverted
problematic changes (.claude/settings.json, BlogPost.model.js) that violated
inst_038/inst_064.

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

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

src/middleware/auth.middleware.js

@@ -66,6 +66,10 @@ async function authenticateToken(req, res, next) {
 
 /**
  * Check if user has required role
+ *
+ * Role-based access control (RBAC) middleware
+ * Verifies that the authenticated user possesses at least one of the required roles
+ * before allowing access to protected routes
  */
 function requireRole(...roles) {
   return (req, res, next) => {