web-player: app chrome (layout, navigation, player)

PlayerExtras is merged into PlayerBar, which now renders volume and
the queue button inline and uses the new Slider (a real range input
with thumb thickness controlled via CSS variables) for both the
progress bar and volume, replacing SeekBar and VolumeControl (grep
confirmed SeekBar's `compact` mode was dead code).

Sidebar and TabsBar migrate to appNavLinks(user, counts?), removing
the duplicated nav links between the two. Decision made without
blocking: Sidebar gains the gradient Logo mark it didn't have before,
for visual consistency with MobileHeader and the login screen.

PlayerDock and MobileHeader's z-index is fixed to z-(--z-sticky)
(they're fixed bars, not menus), and SegmentedControl's to
z-(--z-raised), per the plan's note B.1.5. glass-bar and
theme-transition are applied to PlayerBar (both variants), TabsBar,
Queue and Home (hero/spotlight), replacing duplicated
blur/transition styles.

Verified with npm run check (0 errors) and npm run build; smoke-tested
/login with no console errors. No authenticated visual QA (Docker
unavailable this session).

web-player/src/routes/+page.svelte

@@ -137,7 +137,7 @@
 
 <section class="page-x pt-3 sm:pt-4">
 	<div
-		class="relative overflow-hidden rounded-3xl bg-[image:var(--mf-hero-bg)] px-6 py-8 transition-[background] duration-500 sm:px-9 sm:py-8.5"
+		class="relative overflow-hidden rounded-3xl bg-[image:var(--mf-hero-bg)] px-6 py-8 theme-transition sm:px-9 sm:py-8.5"
 	>
 		<div
 			class="relative flex flex-col items-start gap-7 lg:flex-row lg:flex-wrap lg:items-end lg:justify-between"
@@ -220,7 +220,7 @@
 	{#if spotlight}
 		<section>
 			<div
-				class="grid grid-cols-1 overflow-hidden rounded-panel-lg transition-[background] duration-500 lg:grid-cols-2"
+				class="grid grid-cols-1 overflow-hidden rounded-panel-lg theme-transition lg:grid-cols-2"
 				style="background-image:var(--mf-spotlight-bg), linear-gradient(to right, transparent 50%, color-mix(in oklch, var(--mf-scrim) 22%, transparent) 61%, transparent 92.5%)"
 			>
 				<div class="flex flex-col justify-center p-8 sm:p-9">