Simplify demo notice

frontend/src/App.tsx

@@ -1136,13 +1136,7 @@ export default function App() {
     <div className={`app-shell ${isWorkshopMode && activeModule === "atelier" ? "app-shell--workshop" : ""}`}>
       <main className="workspace">
         <aside className="demo-notice" role="note">
-          <strong>{t("Simulation and demonstration only", "Simulation et demonstration uniquement")}</strong>
-          <span>
-            {t(
-              "This web application is for simulation and demonstration. It must not be used as a validated production MES or safety system.",
-              "Cette application web est destinee a la simulation et a la demonstration. Elle ne doit pas etre utilisee comme MES de production valide ni comme systeme de securite.",
-            )}
-          </span>
+          <strong>Simulation et demonstration uniquement</strong>
         </aside>
 
         <header className="hero">

frontend/src/styles.css

@@ -114,27 +114,21 @@ button:disabled {
 .demo-notice {
   display: flex;
   align-items: center;
-  gap: 12px;
+  justify-content: center;
   padding: 12px 14px;
   border: 1px solid color-mix(in srgb, var(--accent) 46%, #FFFFFF);
   border-radius: 12px;
   background: var(--accent-light);
   color: var(--text-primary);
+  text-align: center;
   box-shadow: 0 1px 3px rgba(10, 47, 90, 0.06), 0 4px 12px rgba(10, 47, 90, 0.04);
 }
 
 .demo-notice strong {
-  flex: 0 0 auto;
   font-family: "Space Grotesk", sans-serif;
   font-size: var(--text-base);
 }
 
-.demo-notice span {
-  color: var(--text-secondary);
-  font-size: var(--text-sm);
-  line-height: 1.45;
-}
-
 .hero,
 .panel,
 .machine-card,