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/layout/AppNavbar.vue

@@ -10,6 +10,16 @@
           tabindex="0"
           class="menu menu-sm dropdown-content mt-3 z-[1] p-3 shadow-lg bg-base-100 rounded-xl w-60 border border-base-300/50"
         >
+          <li class="pt-1 pb-2 lg:hidden">
+            <button
+              class="w-full flex items-center gap-2 rounded-lg px-3 py-2 transition-colors text-base-content/70 hover:bg-primary/8 hover:text-primary"
+              @click="toggleDarkMode"
+            >
+              <IconLucideSun v-if="isDark" class="w-4 h-4" aria-hidden="true" />
+              <IconLucideMoon v-else class="w-4 h-4" aria-hidden="true" />
+              {{ isDark ? 'Mode clair' : 'Mode sombre' }}
+            </button>
+          </li>
           <li class="pt-1 pb-2 lg:hidden">
             <button
               class="w-full flex items-center gap-2 rounded-lg px-3 py-2 transition-colors text-base-content/70 hover:bg-primary/8 hover:text-primary"
@@ -163,6 +173,14 @@
     <!-- Navbar end -->
     <div class="navbar-end">
       <div class="flex items-center gap-1.5">
+        <button
+          class="btn btn-ghost btn-sm btn-circle hidden lg:inline-flex text-base-content/50 hover:text-base-content"
+          :title="isDark ? 'Mode clair' : 'Mode sombre'"
+          @click="toggleDarkMode"
+        >
+          <IconLucideSun v-if="isDark" class="w-4 h-4" aria-hidden="true" />
+          <IconLucideMoon v-else class="w-4 h-4" aria-hidden="true" />
+        </button>
         <button
           class="btn btn-ghost btn-sm btn-circle hidden lg:inline-flex text-base-content/50 hover:text-base-content"
           title="Paramètres d'affichage"
@@ -176,7 +194,7 @@
             <div
               tabindex="0"
               role="button"
-              class="btn btn-ghost btn-circle btn-sm avatar placeholder indicator"
+              class="indicator cursor-pointer"
             >
               <span
                 v-if="unresolvedCount > 0"
@@ -185,9 +203,9 @@
                 {{ unresolvedCount }}
               </span>
               <div
-                class="bg-primary text-primary-content rounded-full w-8 h-8 grid place-items-center"
+                class="bg-primary text-primary-content rounded-full w-8 h-8 flex items-center justify-center"
               >
-                <span class="text-xs font-semibold leading-none tracking-tight">
+                <span class="text-xs font-semibold">
                   {{ activeProfileInitials }}
                 </span>
               </div>
@@ -257,6 +275,8 @@ import IconLucideCpu from '~icons/lucide/cpu'
 import IconLucidePuzzle from '~icons/lucide/puzzle'
 import IconLucidePackage from '~icons/lucide/package'
 import IconLucideLink from '~icons/lucide/link'
+import IconLucideSun from '~icons/lucide/sun'
+import IconLucideMoon from '~icons/lucide/moon'
 import logoSrc from '~/assets/LOGO_CARRE_BLANC.png'
 
 defineEmits<{
@@ -334,6 +354,7 @@ const { openDropdown, setDropdown, scheduleDropdownClose, toggleDropdown } = use
 const { activeProfile } = useProfileSession()
 const { isAdmin, canEdit } = usePermissions()
 const { fetchUnresolvedCount } = useComments()
+const { isDark, toggle: toggleDarkMode, init: initDarkMode } = useDarkMode()
 
 const unresolvedCount = ref(0)
 let pollInterval: ReturnType<typeof setInterval> | null = null
@@ -344,6 +365,7 @@ const refreshUnresolvedCount = async () => {
 }
 
 onMounted(() => {
+  initDarkMode()
   refreshUnresolvedCount()
   pollInterval = setInterval(refreshUnresolvedCount, 60_000)
 })