fix: Checkbox in Sichtbare-Bereiche-Modal jetzt zuverlässig sichtbar (custom statt native, appearance:none umgangen)

frontend/src/App.jsx

@@ -2490,18 +2490,27 @@ function UserManagement({ toast }) {
               {Object.entries(grouped).map(([group, tools]) => (
                 <div key={group} style={{marginBottom:14}}>
                   <div style={{...S.head,marginBottom:6}}>{group}</div>
-                  {tools.map(t => (
-                    <label key={t.id} style={{
+                  {tools.map(t => {
+                    const checked = visSelection.includes(t.id);
+                    return (
+                      <label key={t.id} onClick={()=>toggleVisTool(t.id)} style={{
                         display:'flex',alignItems:'center',gap:8,padding:'6px 2px',cursor:'pointer',
                       }}>
-                      <input type="checkbox" checked={visSelection.includes(t.id)}
-                        onChange={()=>toggleVisTool(t.id)}
-                        style={{width:15,height:15,accentColor:'#ff6b9d',flexShrink:0}}/>
+                        <span style={{
+                          width:16,height:16,borderRadius:4,flexShrink:0,
+                          display:'flex',alignItems:'center',justifyContent:'center',
+                          border:`1px solid ${checked ? '#ff6b9d' : 'rgba(255,255,255,0.3)'}`,
+                          background: checked ? '#ff6b9d' : 'transparent',
+                          transition:'all 0.1s ease',
+                        }}>
+                          {checked && <span style={{color:'#0d0d0f',fontSize:11,fontWeight:700,lineHeight:1}}>✓</span>}
+                        </span>
                         <span style={{color:'rgba(255,255,255,0.75)',fontFamily:'monospace',fontSize:12}}>
                           {t.label}{t.adminOnly ? ' (nur Admin)' : ''}
                         </span>
                       </label>
-                  ))}
+                    );
+                  })}
                 </div>
               ))}
               <div style={{display:'flex',gap:8,marginTop:8}}>