style(frontend): theme-aware scrollbars

Thin scrollbars; thumb uses --border (hover --text-subtle), transparent
track. WebKit + Firefox, follows the active theme.

frontend/src/app.css

@@ -72,3 +72,34 @@ body {
 		transition: none;
 	}
 }
+
+/* Скроллбары в тон темы */
+* {
+	scrollbar-width: thin;
+	scrollbar-color: hsl(var(--border)) transparent;
+}
+
+::-webkit-scrollbar {
+	width: 10px;
+	height: 10px;
+}
+
+::-webkit-scrollbar-track {
+	background: transparent;
+}
+
+::-webkit-scrollbar-thumb {
+	background-color: hsl(var(--border));
+	border: 2px solid transparent;
+	border-radius: 9999px;
+	background-clip: padding-box;
+}
+
+::-webkit-scrollbar-thumb:hover {
+	background-color: hsl(var(--text-subtle));
+	background-clip: padding-box;
+}
+
+::-webkit-scrollbar-corner {
+	background: transparent;
+}