web-player: big pages (Explore, Home) and tracks.ts cleanup

This pass also tackles the task deferred earlier: removing
tracks.ts's TrackTarget wrapper and its 8 accessors
(targetId/targetTitle/targetArtist/targetOwnerUserId/targetExplicit/
targetListensCount/isTargetCurrent/queueItemForTarget/
targetForQueueItem). Explore, Home, Mix, menus.svelte.ts and mixes.ts
now use track objects directly, with
toQueueItem/trackFromQueueItem (new, in player.svelte.ts) as the only
converters. Along the way, TypeScript revealed that isExplicit
doesn't exist in the real /tracks schema: Explore's "explicit" badge
was already a no-op before this refactor (always undefined ??
false); the binding is removed instead of pretending support that
never existed.

Explore: GENRE_INFO/genreTiles are extracted to src/lib/genres.ts;
the search logic
(showGroup/capped/matchPlaylists/searchCounts/searchChips/findTopResult)
is extracted to src/lib/search.ts as pure functions parameterized by
filter/query instead of closing over component state. "Top result"
unifies the duplicated button/link with <svelte:element>. Decision
made without blocking: the 4 group blocks (Tracks/Albums/Users/
Playlists) are not collapsed into a single {#each groups} — each
group has genuinely different snippets, context menu and ListRow
props, and a generic config would have added more indirection than it
removed.

Home: uses Page instead of a hand-rolled page-x; the 3 stats become
an {#each}; the hero/spotlight backgrounds (inline style= with CSS
variables) become the hero-surface/spotlight-surface utilities, and
gap-11.5 is replaced by the --spacing-section token (2.875rem) via
gap-section.

Verified with npm run check (0 errors) and npm run build. /explore
without a session redirects to /login because +layout.server.ts
requires allowAnonymousListening from the backend (unreachable
without Docker this session) — pre-existing behavior, not a
regression. No authenticated visual QA; smoke-tested /login with no
console errors.

web-player/src/routes/(app)/mixes/[id]/+page.svelte

@@ -2,7 +2,13 @@
 	import Play from '@lucide/svelte/icons/play';
 	import Pause from '@lucide/svelte/icons/pause';
 	import Shuffle from '@lucide/svelte/icons/shuffle';
-	import { player, isQueueCurrent, playAllOrToggle, playShuffled } from '$lib/player/player.svelte';
+	import {
+		player,
+		isQueueCurrent,
+		playAllOrToggle,
+		playShuffled,
+		toQueueItem
+	} from '$lib/player/player.svelte';
 	import { fmtTime, plural } from '$lib/format';
 	import Page from '$lib/components/ui/Page.svelte';
 	import BackLink from '$lib/components/ui/BackLink.svelte';
@@ -14,15 +20,14 @@
 	import ContextMenu from '$lib/components/ui/ContextMenu.svelte';
 	import ListPlus from '@lucide/svelte/icons/list-plus';
 	import { createTrackMenu } from '$lib/menus.svelte';
-	import { mixItemTarget } from '$lib/mixes';
-	import { queueItemForTarget } from '$lib/tracks';
+	import { mixItemTrack } from '$lib/mixes';
 
 	let { data, form } = $props();
 
 	const mix = $derived(data.mix);
 	const items = $derived(mix.items);
-	const targets = $derived(items.map(mixItemTarget));
-	const queue = $derived(targets.map(queueItemForTarget));
+	const tracks = $derived(items.map(mixItemTrack));
+	const queue = $derived(tracks.map(toQueueItem));
 	const listTracks = $derived(
 		items.map((item) => ({
 			id: item.trackId,
@@ -97,7 +102,7 @@
 		tracks={listTracks}
 		columns={['plays']}
 		onPlay={playFrom}
-		oncontextmenu={(e, _track, i) => trackMenu.open(e, targets[i])}
+		oncontextmenu={(e, _track, i) => trackMenu.open(e, tracks[i])}
 	/>
 </Page>