fix(sidebar): Navigationspunkte besser lesbar — Kontrast + Trennlinien

- sidebar-section-label: #475569 → rgba(255,255,255,0.38) (Kontrast ~5:1)
- Aktiver Eintrag: color: #60a5fa + font-weight 500 statt #1677ff
- Hover: rgba(255,255,255,0.88) statt #CBD5E1
- Ruhige Items: rgba(255,255,255,0.6) statt #94A3B8
- Child-Items: rgba(255,255,255,0.42), eingerückt 32px
- sidebar-section--bordered: Trennlinie zwischen Sektionsgruppen
- Sektions-Padding leicht erhöht (18px oben)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

management-ui/src/components/Layout/Sidebar.tsx

@@ -130,9 +130,9 @@ export default function Sidebar({ isOpen, onClose }: SidebarProps) {
         <span className="sidebar-logo-text">{t('app.title')}</span>
       </div>
 
-      {NAV.map((section) => (
+      {NAV.map((section, idx) => (
         <div key={section.labelKey}>
-          <div className="sidebar-section">
+          <div className={`sidebar-section${idx > 0 ? ' sidebar-section--bordered' : ''}`}>
             <div className="sidebar-section-label">{t(section.labelKey)}</div>
           </div>
           <ul className="sidebar-menu">