fix(ui): nothing past the right edge of a phone

The Feed's chips + Sort + View row did not fit one line at 375px and pushed
the page 21px wide; the toast stack capped its width by the viewport while
it sits right of the sidebar. The toolbar rows (Feed, Plex browse) wrap,
and the toasts are capped by their host.

frontend/src/components/ui/Toaster.tsx

@@ -111,11 +111,13 @@ export default function Toaster({
     // z-overlay, and catching the click — took play/pause, ±10, stop, prev/next and mute for as long
     // as a toast was up (the connection notice: until the server answered). The same rung UpNextCard
     // uses for the same reason. Clicks between the cards go through to what is underneath.
+    // Its width is capped by its HOST (100%), not the viewport: it sits in the content column, right
+    // of the sidebar, and a 100vw cap pushed it past the right edge of a phone (prod UAT 2026-09-19).
     <div
       // lib/listNav: focus on a toast's Undo is not the reader leaving the list the toast is about.
       data-toast-region=""
       aria-live={isTop && armed ? "polite" : "off"}
-      className={`absolute left-4 z-overlay flex flex-col gap-2 w-80 max-w-[calc(100vw-2rem)] ${
+      className={`absolute left-4 z-overlay flex flex-col gap-2 w-80 max-w-[calc(100%-2rem)] ${
         overlay ? "bottom-24 pointer-events-none" : "bottom-4"
       }`}
       // Inside an overlay, a click on a toast is not a click on the overlay's backdrop.