web-player: headers, dialogs and typography

PageHeader absorbs CollectionHeader
(title/eyebrow/description/meta/cover?/actions?/align?): without a
cover it behaves like the old simple PageHeader (inline actions),
with a cover like the old CollectionHeader (actions below). It sets
its own bottom margin (mb-7/8); the mt-* each page used to add
afterward are removed. Migrates the 9 places that used either one
(albums, library, playlists, upload, Explore x2, liked, mix,
profile). CollectionHeader is removed.

AlbumHeader and PlaylistHeader are inlined into their pages and
removed. Decision (recommended, not blocking): PlaylistHeader gains
icons on Edit/Delete/Play, matching what AlbumHeader already had.

New ConfirmDialog replaces the two delete dialogs (album and
playlist), which had different typography. Modal now uses
.glass-panel (instead of duplicating the inline style=) and
z-(--z-modal); its eyebrow and title use the
text-eyebrow/text-display-3 recipes.

SectionHeading gains `count?` (a "N results" line, replacing 4 copies
in Explore) and `href?`/`linkLabel?` ("See all", replacing Home's).
Applies typography recipes (text-display-2/3, text-eyebrow,
text-body) and width tokens (max-w-prose-sm, max-w-hero) across
EmptyState, +error, "No results", and the Home/Queue/Sidebar hero and
stats. The "You haven't listened to anything yet" empty state
(duplicated twice on Home) becomes a local snippet.

Verified with npm run check/build; no authenticated visual QA (Docker
unavailable this session).

web-player/src/lib/components/ui/SectionHeading.svelte

@@ -1,18 +1,32 @@
 <script lang="ts">
 	import type { Snippet } from 'svelte';
+	import { plural } from '$lib/format';
 
 	interface Props {
 		title: string;
 		subtitle?: string;
+		count?: number;
+		href?: string;
+		linkLabel?: string;
 		class?: string;
 		actions?: Snippet;
 	}
 
-	let { title, subtitle, class: klass = '', actions }: Props = $props();
+	let {
+		title,
+		subtitle,
+		count,
+		href,
+		linkLabel = 'Ver todas',
+		class: klass = '',
+		actions
+	}: Props = $props();
+
+	const hasActions = $derived(!!actions || count !== undefined || !!href);
 </script>
 
 {#snippet heading()}
-	<h2 class="font-display text-lg font-medium tracking-tight text-fg">
+	<h2 class="text-display-4 text-fg">
 		{title}
 	</h2>
 	{#if subtitle}
@@ -20,10 +34,31 @@
 	{/if}
 {/snippet}
 
-{#if actions}
+{#snippet autoActions()}
+	{#if count !== undefined}
+		<div class="h-px flex-1 self-center bg-line"></div>
+		<span class="shrink-0 text-xs text-muted tabular-nums">
+			{plural(count, 'resultado', 'resultados')}
+		</span>
+	{/if}
+	{#if href}
+		<a
+			{href}
+			class="shrink-0 text-xs font-medium tracking-wider text-fg-3 uppercase transition-colors hover:text-fg"
+		>
+			{linkLabel}
+		</a>
+	{/if}
+{/snippet}
+
+{#if hasActions}
 	<div class="mb-4 flex items-end justify-between gap-4 sm:mb-4.5 {klass}">
 		<div>{@render heading()}</div>
-		{@render actions()}
+		{#if actions}
+			{@render actions()}
+		{:else}
+			{@render autoActions()}
+		{/if}
 	</div>
 {:else}
 	<div class="mb-4 sm:mb-4.5 {klass}">