feat(admin): replace checkbox with toggle-switch slider, add i18n multilanguage

frontend/styles.css

@@ -604,6 +604,49 @@ table.admin-table tbody tr:hover {
     filter: brightness(1.1);
 }
 
+/* ---------------- Forms / Toggle Switch ---------------- */
+.toggle-switch {
+    position: relative;
+    display: inline-block;
+    width: 44px;
+    height: 24px;
+    flex-shrink: 0;
+}
+.toggle-switch input {
+    opacity: 0;
+    width: 0;
+    height: 0;
+}
+.toggle-slider {
+    position: absolute;
+    cursor: pointer;
+    top: 0; left: 0; right: 0; bottom: 0;
+    background-color: var(--line);
+    transition: background-color 0.3s ease;
+    border-radius: 24px;
+}
+.toggle-slider:before {
+    position: absolute;
+    content: "";
+    height: 16px;
+    width: 16px;
+    left: 4px;
+    bottom: 4px;
+    background-color: var(--text);
+    transition: transform 0.3s cubic-bezier(0.4, 0.0, 0.2, 1);
+    border-radius: 50%;
+}
+input:checked + .toggle-slider {
+    background-color: var(--accent);
+}
+input:focus + .toggle-slider {
+    box-shadow: 0 0 0 2px var(--bg-card), 0 0 0 4px var(--accent);
+}
+input:checked + .toggle-slider:before {
+    transform: translateX(20px);
+    background-color: #111;
+}
+
 /* Admin tabs */
 .admin-tabs { 
     display: flex; gap: 0.4rem;