added dark mode support across components and improved accessibility styling

frontend/src/components/CronSlider.vue

@@ -20,10 +20,10 @@ async function update() {
 }
 </script>
 <template>
-  <div class="p-4 bg-white rounded shadow">
+  <div class="p-4 bg-white dark:bg-gray-800 rounded shadow dark:shadow-gray-700 dark:text-gray-200">
     <label class="block font-semibold mb-2">Fetch Interval (Stunden)</label>
     <input type="range" min="0.5" max="24" step="0.5" v-model="hours" @change="update"
-           class="w-full"/>
+           class="w-full accent-green-600 dark:accent-green-500"/>
     <p class="text-sm mt-2">{{ hours }} h <span v-if="saving" class="animate-pulse">…</span></p>
   </div>
 </template>