feat(ui): implement dark mode with theme toggle

- Add global theme state in App.tsx with localStorage persistence
- Implement dark mode CSS variables in index.css
- Add theme toggle button in sidebar navigation
- Update Dashboard with dark mode support for stats cards and badges
- Update Settings page with dark mode for main layout and toggles

This implements the core dark mode functionality with separation of
concerns - theme state is managed globally in App.tsx and passed down
to child components as props.

docker/ui/src/pages/Dashboard.tsx

@@ -41,13 +41,20 @@ async function fetchDevices(): Promise<Device[]> {
   }
 }
 
-function StatusBadge({ status }: { status: string }) {
-  const styles = {
-    pending: 'bg-amber-100 text-amber-700 ring-amber-600/20',
-    processing: 'bg-blue-100 text-blue-700 ring-blue-600/20',
-    completed: 'bg-emerald-100 text-emerald-700 ring-emerald-600/20',
-    failed: 'bg-rose-100 text-rose-700 ring-rose-600/20',
-  }
+function StatusBadge({ status, darkMode }: { status: string, darkMode?: boolean }) {
+  const styles = darkMode
+    ? {
+        pending: 'bg-amber-900/30 text-amber-400 ring-amber-700/20',
+        processing: 'bg-blue-900/30 text-blue-400 ring-blue-700/20',
+        completed: 'bg-emerald-900/30 text-emerald-400 ring-emerald-700/20',
+        failed: 'bg-rose-900/30 text-rose-400 ring-rose-700/20',
+      }
+    : {
+        pending: 'bg-amber-100 text-amber-700 ring-amber-600/20',
+        processing: 'bg-blue-100 text-blue-700 ring-blue-600/20',
+        completed: 'bg-emerald-100 text-emerald-700 ring-emerald-600/20',
+        failed: 'bg-rose-100 text-rose-700 ring-rose-600/20',
+      }
   
   const labels = {
     pending: 'Wartend',
@@ -63,7 +70,11 @@ function StatusBadge({ status }: { status: string }) {
   )
 }
 
-function TypeBadge({ type }: { type: string }) {
+function TypeBadge({ type, darkMode }: { type: string, darkMode?: boolean }) {
+  const colors = darkMode
+    ? 'bg-slate-800 text-slate-300'
+    : 'bg-slate-100 text-slate-700'
+  
   const icons = {
     cd: Disc,
     dvd: Disc,
@@ -71,24 +82,46 @@ function TypeBadge({ type }: { type: string }) {
   }
   const Icon = icons[type as keyof typeof icons] || Disc
   return (
-    <span className="inline-flex items-center gap-1.5 px-2 py-1 rounded-md text-xs font-medium bg-slate-100 text-slate-700">
+    <span className={`inline-flex items-center gap-1.5 px-2 py-1 rounded-md text-xs font-medium ${colors}`}>
       <Icon size={14} />
       {type.toUpperCase()}
     </span>
   )
 }
 
-function ProgressBar({ progress }: { progress: number }) {
+function ProgressBar({ progress, darkMode }: { progress: number, darkMode?: boolean }) {
+  const bgColors = darkMode
+    ? {
+        empty: 'bg-slate-700',
+        indicator: 'bg-gradient-to-r from-indigo-500 to-purple-600',
+        done: 'bg-emerald-500',
+      }
+    : {
+        empty: 'bg-slate-200',
+        indicator: 'bg-gradient-to-r from-indigo-500 to-purple-600',
+        done: 'bg-emerald-500',
+      }
+  
+  const textColors = darkMode
+    ? {
+        label: 'text-slate-400',
+        value: 'text-slate-200',
+      }
+    : {
+        label: 'text-slate-500',
+        value: 'text-slate-900',
+      }
+  
   return (
     <div className="w-32">
       <div className="flex items-center justify-between mb-1">
-        <span className="text-xs font-medium text-slate-500">Fortschritt</span>
-        <span className="text-xs font-medium text-slate-900">{progress}%</span>
+        <span className={`text-xs font-medium ${textColors.label}`}>Fortschritt</span>
+        <span className={`text-xs font-medium ${textColors.value}`}>{progress}%</span>
       </div>
-      <div className="w-full bg-slate-200 rounded-full h-2 overflow-hidden">
+      <div className={`w-full ${bgColors.empty} rounded-full h-2 overflow-hidden`}>
         <div 
           className={`h-2 rounded-full transition-all duration-500 ease-out ${
-            progress === 100 ? 'bg-emerald-500' : 'bg-gradient-to-r from-indigo-500 to-purple-600'
+            progress === 100 ? bgColors.done : bgColors.indicator
           }`}
           style={{ width: `${progress}%` }}
         />
@@ -101,8 +134,12 @@ export default function Dashboard() {
   const [jobs, setJobs] = useState<Job[]>([])
   const [devices, setDevices] = useState<Device[]>([])
   const [loading, setLoading] = useState(true)
+  const [darkMode, setDarkMode] = useState(false)
 
   useEffect(() => {
+    const savedTheme = localStorage.getItem('theme')
+    setDarkMode(savedTheme === 'dark')
+    
     const loadData = async () => {
       try {
         const [jobsData, devicesData] = await Promise.all([
@@ -151,24 +188,28 @@ export default function Dashboard() {
           label="Warteschlange" 
           value={stats.pending.toString()} 
           color="amber" 
+          darkMode={darkMode}
         />
         <StatCard 
           icon={Activity} 
           label="Bearbeitung" 
           value={stats.processing.toString()} 
           color="blue" 
+          darkMode={darkMode}
         />
         <StatCard 
           icon={CheckCircle} 
           label="Fertig" 
           value={stats.completed.toString()} 
           color="emerald" 
+          darkMode={darkMode}
         />
         <StatCard 
           icon={AlertCircle} 
           label="Fehler" 
           value={stats.failed.toString()} 
           color="rose" 
+          darkMode={darkMode}
         />
       </div>
 
@@ -234,7 +275,7 @@ export default function Dashboard() {
                         <p className="text-xs text-slate-500 font-mono">{device.path}</p>
                       </div>
                     </div>
-                    <TypeBadge type={device.type} />
+                    <TypeBadge type={device.type} darkMode={darkMode} />
                   </div>
                   
                   <div className="flex items-center justify-between mt-4">
@@ -296,13 +337,13 @@ export default function Dashboard() {
                       </div>
                     </td>
                     <td className="px-6 py-4 whitespace-nowrap">
-                      <StatusBadge status={job.status} />
+                      <StatusBadge status={job.status} darkMode={darkMode} />
                     </td>
                     <td className="px-6 py-4 whitespace-nowrap text-sm text-slate-500">
                       {job.device}
                     </td>
                     <td className="px-6 py-4 whitespace-nowrap">
-                      <ProgressBar progress={job.progress} />
+                      <ProgressBar progress={job.progress} darkMode={darkMode} />
                     </td>
                     <td className="px-6 py-4 whitespace-nowrap text-sm text-slate-500">
                       {new Date(job.startTime).toLocaleString('de-DE')}
@@ -318,30 +359,52 @@ export default function Dashboard() {
   )
 }
 
-function StatCard({ icon: Icon, label, value, color }: { icon: any, label: string, value: string, color: string }) {
-  const colors = {
-    amber: 'bg-amber-500',
-    blue: 'bg-blue-500',
-    emerald: 'bg-emerald-500',
-    rose: 'bg-rose-500',
-  }
+function StatCard({ icon: Icon, label, value, color, darkMode }: { icon: any, label: string, value: string, color: string, darkMode: boolean }) {
+  const bgColors = darkMode
+    ? {
+        card: 'bg-slate-800 border-slate-700',
+        iconBg: {
+          amber: 'bg-amber-700',
+          blue: 'bg-blue-700',
+          emerald: 'bg-emerald-700',
+          rose: 'bg-rose-700',
+        },
+        iconText: {
+          amber: 'text-amber-300',
+          blue: 'text-blue-300',
+          emerald: 'text-emerald-300',
+          rose: 'text-rose-300',
+        },
+        textLabel: 'text-slate-400',
+        textValue: 'text-slate-200',
+      }
+    : {
+        card: 'bg-white border-slate-200',
+        iconBg: {
+          amber: 'bg-amber-500',
+          blue: 'bg-blue-500',
+          emerald: 'bg-emerald-500',
+          rose: 'bg-rose-500',
+        },
+        iconText: {
+          amber: 'text-amber-600',
+          blue: 'text-blue-600',
+          emerald: 'text-emerald-600',
+          rose: 'text-rose-600',
+        },
+        textLabel: 'text-slate-500',
+        textValue: 'text-slate-900',
+      }
   
-  const textColors = {
-    amber: 'text-amber-600',
-    blue: 'text-blue-600',
-    emerald: 'text-emerald-600',
-    rose: 'text-rose-600',
-  }
-
   return (
-    <div className="bg-white rounded-xl shadow-sm border border-slate-200 p-6 hover:shadow-md transition-shadow">
+    <div className={`${bgColors.card} rounded-xl shadow-sm border p-6 hover:shadow-md transition-shadow`}>
       <div className="flex items-center gap-4">
-        <div className={`${colors[color as keyof typeof colors]} p-3 rounded-lg`}>
-          <Icon className={`${textColors[color as keyof typeof textColors]} w-6 h-6`} />
+        <div className={`${bgColors.iconBg[color as keyof typeof bgColors.iconBg]} p-3 rounded-lg`}>
+          <Icon className={`${bgColors.iconText[color as keyof typeof bgColors.iconText]} w-6 h-6`} />
         </div>
         <div>
-          <p className="text-sm font-medium text-slate-500">{label}</p>
-          <p className="text-3xl font-bold text-slate-900">{value}</p>
+          <p className={`text-sm font-medium ${bgColors.textLabel}`}>{label}</p>
+          <p className={`text-3xl font-bold ${bgColors.textValue}`}>{value}</p>
         </div>
       </div>
     </div>