feat(ui) : add site colors, dark mode toggle and card styling improvements

- Site color field with color picker in create/edit modals
- Dark mode theme (mytheme-dark) with toggle in navbar
- Stronger site color visibility on cards (gradient, top border, badges)
- Bigger action buttons (btn-sm) on machine cards
- White card backgrounds with proper dark mode support

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

app/components/ComponentHierarchy.vue

@@ -5,11 +5,13 @@
       <ComponentItem
         :component="component"
         :is-edit-mode="isEditMode"
+        :show-delete="showDelete"
         :collapse-all="collapseAll"
         :toggle-token="toggleToken"
         @update="$emit('update', $event)"
         @edit-piece="$emit('edit-piece', $event)"
         @custom-field-update="$emit('custom-field-update', $event)"
+        @delete="$emit('delete')"
       />
     </div>
   </div>
@@ -27,6 +29,10 @@ defineProps({
     type: Boolean,
     default: false
   },
+  showDelete: {
+    type: Boolean,
+    default: false
+  },
   collapseAll: {
     type: Boolean,
     default: true
@@ -37,5 +43,5 @@ defineProps({
   }
 })
 
-defineEmits(['update', 'edit-piece', 'custom-field-update'])
+defineEmits(['update', 'edit-piece', 'custom-field-update', 'delete'])
 </script>