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/NavDrawer.js

@@ -1,5 +1,6 @@
 import React from 'react';
-import { X, Home, BarChart2, BookOpen, Download, ShieldCheck } from 'lucide-react';
+import { X, Home, BarChart2, BookOpen, Download, ShieldCheck, Settings } from 'lucide-react';
+import { useAuth } from '../contexts/AuthContext';
 
 const NAV_ITEMS = [
   { id: 'home',           label: 'Home',           icon: Home,        color: '#0EA5E9', description: 'Main dashboard'            },
@@ -9,7 +10,11 @@ const NAV_ITEMS = [
   { id: 'exports',        label: 'Exports',        icon: Download,    color: '#8B5CF6', description: 'Export data & reports'      },
 ];
 
+const ADMIN_ITEM = { id: 'admin', label: 'Admin Panel', icon: Settings, color: '#EF4444', description: 'User management & audit' };
+
 export default function NavDrawer({ isOpen, onClose, currentPage, onNavigate }) {
+  const { isAdmin } = useAuth();
+
   if (!isOpen) return null;
 
   return (
@@ -110,6 +115,60 @@ export default function NavDrawer({ isOpen, onClose, currentPage, onNavigate })
               </button>
             );
           })}
+
+          {/* Admin panel link — visible only to Admin group */}
+          {isAdmin() && (() => {
+            const { id, label, icon: Icon, color, description } = ADMIN_ITEM;
+            const active = currentPage === id;
+            return (
+              <button
+                key={id}
+                onClick={() => { onNavigate(id); onClose(); }}
+                style={{
+                  display: 'flex', alignItems: 'center', gap: '0.875rem',
+                  padding: '0.75rem 0.875rem',
+                  borderRadius: '0.5rem',
+                  border: active ? `1px solid ${color}50` : '1px solid transparent',
+                  background: active ? `${color}18` : 'transparent',
+                  cursor: 'pointer', textAlign: 'left', width: '100%',
+                  marginTop: '0.5rem',
+                  borderTop: '1px solid rgba(255, 255, 255, 0.05)',
+                  paddingTop: '1rem',
+                  transition: 'background 0.15s, border-color 0.15s'
+                }}
+                onMouseEnter={e => { if (!active) e.currentTarget.style.background = 'rgba(255,255,255,0.04)'; }}
+                onMouseLeave={e => { if (!active) e.currentTarget.style.background = 'transparent'; }}
+              >
+                <div style={{
+                  width: '36px', height: '36px', flexShrink: 0,
+                  borderRadius: '0.375rem',
+                  background: `${color}18`,
+                  border: `1px solid ${color}40`,
+                  display: 'flex', alignItems: 'center', justifyContent: 'center'
+                }}>
+                  <Icon style={{ width: '17px', height: '17px', color }} />
+                </div>
+                <div style={{ flex: 1, minWidth: 0 }}>
+                  <div style={{
+                    fontFamily: 'monospace', fontSize: '0.8rem', fontWeight: '600',
+                    color: active ? color : '#CBD5E1',
+                    textTransform: 'uppercase', letterSpacing: '0.06em'
+                  }}>
+                    {label}
+                  </div>
+                  <div style={{ fontSize: '0.68rem', color: '#475569', marginTop: '1px' }}>
+                    {description}
+                  </div>
+                </div>
+                {active && (
+                  <div style={{
+                    width: '6px', height: '6px', borderRadius: '50%',
+                    background: color, boxShadow: `0 0 8px ${color}`, flexShrink: 0
+                  }} />
+                )}
+              </button>
+            );
+          })()}
         </nav>
 
         {/* Footer */}