feat: implement group-based access control (Admin, Standard_User, Leadership, Read_Only)

- Add user_group migration and created_by column migration
- Replace requireRole middleware with requireGroup
- Update all backend routes to use group-based authorization
- Add Standard_User conditional delete with ownership, state, and compliance checks
- Add cascade impact check for CVE deletes
- Update AuthContext with group-based permission helpers
- Update all frontend components for group-based rendering
- Update UserManagement UI with group dropdown, confirmation dialogs, self-demotion prevention

frontend/src/components/UserMenu.js

@@ -19,17 +19,26 @@ export default function UserMenu({ onManageUsers, onAuditLog }) {
         return () => document.removeEventListener('mousedown', handleClickOutside);
     }, []);
 
-    const getRoleBadgeColor = (role) => {
-        switch (role) {
-            case 'admin':
+    const getGroupBadgeColor = (group) => {
+        switch (group) {
+            case 'Admin':
                 return 'bg-red-100 text-red-800';
-            case 'editor':
+            case 'Standard_User':
                 return 'bg-blue-100 text-blue-800';
+            case 'Leadership':
+                return 'bg-purple-100 text-purple-800';
+            case 'Read_Only':
+                return 'bg-gray-100 text-gray-800';
             default:
                 return 'bg-gray-100 text-gray-800';
         }
     };
 
+    const formatGroupName = (group) => {
+        if (!group) return '';
+        return group.replace(/_/g, ' ');
+    };
+
     const handleLogout = async () => {
         setIsOpen(false);
         await logout();
@@ -62,7 +71,7 @@ export default function UserMenu({ onManageUsers, onAuditLog }) {
                 </div>
                 <div className="text-left hidden sm:block">
                     <p className="text-sm font-medium text-gray-900">{user.username}</p>
-                    <p className="text-xs text-gray-500 capitalize">{user.role}</p>
+                    <p className="text-xs text-gray-500">{formatGroupName(user.group)}</p>
                 </div>
                 <ChevronDown className={`w-4 h-4 text-gray-500 transition-transform ${isOpen ? 'rotate-180' : ''}`} />
             </button>
@@ -72,8 +81,8 @@ export default function UserMenu({ onManageUsers, onAuditLog }) {
                     <div className="px-4 py-3 border-b border-gray-100">
                         <p className="text-sm font-medium text-gray-900">{user.username}</p>
                         <p className="text-sm text-gray-500">{user.email}</p>
-                        <span className={`inline-block mt-2 px-2 py-1 rounded text-xs font-medium ${getRoleBadgeColor(user.role)}`}>
-                            {user.role.charAt(0).toUpperCase() + user.role.slice(1)}
+                        <span className={`inline-block mt-2 px-2 py-1 rounded text-xs font-medium ${getGroupBadgeColor(user.group)}`}>
+                            {formatGroupName(user.group)}
                         </span>
                     </div>