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/machines/index.vue

@@ -65,7 +65,11 @@
         <div
           v-for="machine in filteredMachines"
           :key="machine.id"
-          class="card bg-base-100 shadow-sm hover:shadow-xl transition-shadow cursor-pointer"
+          class="card site-card shadow-md hover:shadow-xl transition-shadow cursor-pointer overflow-hidden"
+          :style="{
+            borderTop: machine.site?.color ? `4px solid ${machine.site.color}` : '4px solid transparent',
+            background: machine.site?.color ? `linear-gradient(160deg, ${machine.site.color}30 0%, ${machine.site.color}08 40%, var(--color-base-100) 100%)` : undefined,
+          }"
           @click="viewMachineDetails(machine)"
         >
           <div class="card-body flex flex-col">
@@ -77,8 +81,11 @@
 
             <div class="space-y-2 text-sm">
               <div class="flex items-center gap-2">
-                <IconLucideMapPin class="w-4 h-4 text-blue-500" aria-hidden="true" />
-                <span class="text-gray-600">{{ machine.site?.name || 'Site inconnu' }}</span>
+                <IconLucideMapPin class="w-4 h-4" :style="{ color: machine.site?.color || '#3b82f6' }" aria-hidden="true" />
+                <span
+                  class="font-bold text-sm px-2.5 py-1 rounded-lg text-base-content"
+                  :style="machine.site?.color ? { backgroundColor: machine.site.color + '30', border: `1px solid ${machine.site.color}40` } : {}"
+                >{{ machine.site?.name || 'Site inconnu' }}</span>
               </div>
 
               <div v-if="machine.reference" class="flex items-center gap-2">
@@ -88,13 +95,13 @@
             </div>
 
             <div class="mt-auto pt-3 flex items-center justify-end gap-2">
-              <button v-if="canEdit" class="btn btn-ghost btn-xs" @click.stop="editMachine(machine)">
+              <button v-if="canEdit" class="btn btn-ghost btn-sm" @click.stop="editMachine(machine)">
                 Modifier
               </button>
-              <button v-if="canEdit" class="btn btn-ghost btn-xs text-error" @click.stop="confirmDeleteMachine(machine)">
+              <button v-if="canEdit" class="btn btn-ghost btn-sm text-error" @click.stop="confirmDeleteMachine(machine)">
                 Supprimer
               </button>
-              <NuxtLink :to="`/machine/${machine.id}`" class="btn btn-primary btn-xs">
+              <NuxtLink :to="`/machine/${machine.id}`" class="btn btn-primary btn-sm">
                 Détails
               </NuxtLink>
             </div>