refactor(ui) : improve styling, layout and responsive across all components

Rework CSS theme (app.css), navbar layout, dashboard page, machine detail,
catalog pages, and various form/display components for better consistency
and mobile responsiveness.

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

app/pages/constructeurs.vue

@@ -15,7 +15,7 @@
       </button>
     </div>
 
-    <div class="card bg-base-100 shadow-lg">
+    <div class="card bg-base-100 shadow-sm">
       <div class="card-body space-y-4">
         <DataTable
           :columns="columns"