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/pages/machine/[id].vue

@@ -39,7 +39,11 @@
         rounded
       >
         <div class="flex justify-center gap-4">
-          <div v-if="d.machine.value.site?.name" class="badge badge-outline">
+          <div
+            v-if="d.machine.value.site?.name"
+            class="badge badge-outline font-semibold"
+            :style="d.machine.value.site?.color ? { borderColor: d.machine.value.site.color + '60', backgroundColor: d.machine.value.site.color + '25', color: d.machine.value.site.color } : {}"
+          >
             {{ d.machine.value.site?.name }}
           </div>
           <div v-if="d.machine.value.reference" class="badge badge-outline">