fix(scrollbar): force overflow-y: scroll in .app-scrollbar utility

The favorites and recent views had local #id { overflow-y: auto }
which has higher CSS specificity than the global .app-scrollbar class.
On macOS, overflow-y: auto means overlay scrollbars that auto-fade,
so the gutter and themed thumb were never reserved.

Bake overflow-y: scroll into the utility itself (its whole purpose) and
drop the now-redundant overflow-y: auto from the two local rules.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Entire-Checkpoint: b2d2124cd992

apps/web/src/styles.scss

@@ -30,6 +30,7 @@
 // Always-visible themed scrollbar. Apply to scroll containers that should
 // reserve gutter and not rely on macOS overlay scrollbars (which auto-fade).
 .app-scrollbar {
+    overflow-y: scroll;
     scrollbar-gutter: stable;
     scrollbar-width: thin;
     scrollbar-color: color-mix(in srgb, var(--app-muted-color) 55%, transparent)

libs/ui/components/src/lib/channel-list-container/favorites-view/favorites-view.component.scss

@@ -9,7 +9,6 @@
     flex: 1;
     min-height: 0;
     overflow-x: hidden;
-    overflow-y: auto;
 }
 
 .channel-list {

libs/ui/components/src/lib/channel-list-container/recent-view/recent-view.component.scss

@@ -9,7 +9,6 @@
     flex: 1;
     min-height: 0;
     overflow-x: hidden;
-    overflow-y: auto;
 }
 
 .channel-list {