feat: Add theme-aware custom scrollbars

Thin 6px scrollbars using design tokens (--border, --muted-foreground)
so they blend properly in both light and dark mode. Uses standard
scrollbar-width/scrollbar-color plus WebKit pseudo-elements for
cross-browser coverage.

apps/web/src/index.css

@@ -336,6 +336,38 @@ select:focus-visible {
   }
 }
 
+/* Custom scrollbars */
+* {
+  scrollbar-width: thin;
+  scrollbar-color: hsl(var(--border)) transparent;
+}
+
+*:hover {
+  scrollbar-color: hsl(var(--muted-foreground) / 0.35) transparent;
+}
+
+::-webkit-scrollbar {
+  width: 6px;
+  height: 6px;
+}
+
+::-webkit-scrollbar-track {
+  background: transparent;
+}
+
+::-webkit-scrollbar-thumb {
+  background-color: hsl(var(--border));
+  border-radius: 3px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+  background-color: hsl(var(--muted-foreground) / 0.5);
+}
+
+::-webkit-scrollbar-corner {
+  background: transparent;
+}
+
 @layer base {
   * {
     @apply border-border;