Erreur camera: overlay plein ecran + pas de fallback webcam

Page splash au boot pour eviter l'erreur Firefox

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/css/style.css

@@ -1215,6 +1215,39 @@ h3 {
   border-radius: 3px;
 }
 
+/* === Erreur camera === */
+.camera-erreur {
+  position: fixed;
+  top: 0; left: 0;
+  width: 100%; height: 100%;
+  background: rgba(0, 0, 0, 0.9);
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  z-index: 999;
+  gap: 1.5rem;
+}
+
+.camera-erreur-icon {
+  font-size: 6rem;
+  opacity: 0.5;
+}
+
+.camera-erreur p {
+  font-size: 1.8rem;
+  font-weight: 600;
+  color: #fff;
+  text-align: center;
+  padding: 0 2rem;
+}
+
+.camera-erreur-sub {
+  font-size: 1.1rem;
+  color: #888;
+  animation: pulse 1.5s infinite;
+}
+
 /* === Clavier virtuel email === */
 .clavier-virtuel {
   display: flex;