fix: CSP compliance for inline styles and scripts

includes/header.php

@@ -74,7 +74,7 @@
         <button id="theme-toggle" class="icon-button" aria-label="Basculer entre mode clair et sombre" title="Changer le thème">
             <i class="fas fa-sun" aria-hidden="true"></i>
         </button>
-        <button id="install-pwa" class="icon-button install-pwa-button" style="display: none;" nonce="<?php echo getCspNonce(); ?>" aria-label="Installer l'application">
+        <button id="install-pwa" class="icon-button install-pwa-button is-hidden" aria-label="Installer l'application">
             <i class="fas fa-download" aria-hidden="true"></i>
         </button>
         <button class="mobile-menu-toggle" aria-expanded="false" aria-controls="mobile-menu" aria-label="Ouvrir le menu de navigation">

includes/pwa-init.php

@@ -55,7 +55,7 @@ function addPWAScripts() {
             
             // Afficher le bouton d'installation s'il existe
             if (installButton) {
-                installButton.style.display = 'block';
+                installButton.classList.remove('is-hidden');
                 installButton.addEventListener('click', function() {
                     deferredPrompt.prompt();
                     deferredPrompt.userChoice.then(function(choiceResult) {
@@ -63,7 +63,7 @@ function addPWAScripts() {
                             console.log('PWA installée');
                         }
                         deferredPrompt = null;
-                        installButton.style.display = 'none';
+                        installButton.classList.add('is-hidden');
                     });
                 });
             }
@@ -73,7 +73,7 @@ function addPWAScripts() {
         window.addEventListener('appinstalled', function() {
             console.log('PWA installée avec succès');
             if (installButton) {
-                installButton.style.display = 'none';
+                installButton.classList.add('is-hidden');
             }
         });
     </script>