Scroll content inside the shell so the player shares the ambient backdrop

The player dock used to sit fixed over the scrolling page, so it needed an
opaque background. The shell is now a fixed-height frame where only the
content column scrolls, letting the dock stay transparent like the sidebar
and queue. Scroll reset/restore on navigation moves to restoreScroll(), and
the stable scrollbar gutter moves from <html> to the content scroller.

web-player/src/lib/components/player/Queue.svelte

@@ -43,8 +43,8 @@
 	inert={!queuePanel.open}
 >
 	<aside
-		class="flex shrink-0 flex-col border-l border-hairline px-4 pt-5"
-		style="width:var(--mf-queue-w); padding-bottom:calc(var(--mf-player-h) + 2rem)"
+		class="flex min-h-0 shrink-0 flex-col border-l border-hairline px-4 pt-5 pb-5"
+		style="width:var(--mf-queue-w)"
 	>
 		<div class="mb-5 flex items-center justify-between">
 			<h2 class="font-display text-base font-medium tracking-tight text-fg">En cola</h2>
@@ -82,7 +82,7 @@
 
 		<!-- svelte-ignore a11y_no_static_element_interactions -->
 		<div
-			class="flex flex-1 flex-col gap-px overflow-y-auto"
+			class="flex min-h-0 flex-1 flex-col gap-px overflow-y-auto"
 			ondragover={(event) => dragFrom !== null && event.preventDefault()}
 			ondrop={onDrop}
 		>