web-player: TypeScript helpers (partial)

Add src/lib/actions/pressable.ts and clickOutside.ts (Svelte actions;
role/tabindex stay static in markup for SSR accessibility, the action
only adds click + Enter/Space) and src/lib/toggle.svelte.ts
(createToggle), used by playlists.svelte.ts and queuePanel.svelte.ts.

format.ts: adds plural(n, one, many); migrates the repo's 15 manual
pluralizations, unifying them to lowercase (visible diff in
Playlists, Home, liked, Explore).

player.svelte.ts: adds toQueueItem, isQueueCurrent, playAllOrToggle,
playShuffled; renames addToQueue -> playNextItem (the old name was
misleading: it inserts next, not at the end). Migrates the 5 places
that repeated the isCurrentQueue/playAll pattern (album, playlist,
liked, mix, Home). Simplifies liked.svelte.ts and recentlyPlayed.ts
with object spread instead of rebuilding every field by hand.

navigation.svelte.ts: adds searchHref (migrates the duplicated
buildHref from TopBar and Explore) and appNavLinks (added; its
adoption in Sidebar/TabsBar is left for a later pass, as noted
there).

menus.svelte.ts: createTrackMenu() replaces the manual context-menu
state (contextMenu + contextMenuStateFor + addToQueue) in Home,
Explore and Mix.

Deliberately left pending: removing tracks.ts's TrackTarget wrapper
and its 8 accessors is deferred — it's the riskiest change in the
plan, touches types across Home/Explore/Mix/menus, and couldn't be
visually verified without Docker this session.

Verified with npm run check/build.

web-player/src/lib/player/player.svelte.ts

@@ -1,6 +1,7 @@
 import { browser } from '$app/environment';
 import { DEFAULT_ACCENT } from '$lib/theme/color';
 import { extractAccent, type Accent } from '$lib/theme/palette';
+import { shuffle } from '$lib/collections';
 
 export interface PlayerTrack {
 	id: string | number;
@@ -47,6 +48,25 @@ export function toQueueItems(tracks: ApiTrackLike[]): QueueItem[] {
 	}));
 }
 
+export function toQueueItem(track: ApiTrackLike): QueueItem {
+	return toQueueItems([track])[0];
+}
+
+export function isQueueCurrent(items: { id: string | number }[]): boolean {
+	return items.some((item) => item.id === player.current.id);
+}
+
+export function playAllOrToggle(items: QueueItem[]) {
+	if (items.length === 0) return;
+	if (isQueueCurrent(items)) player.toggle();
+	else player.playQueue(items, 0);
+}
+
+export function playShuffled(items: QueueItem[]) {
+	if (items.length === 0) return;
+	player.playQueue(shuffle(items), 0);
+}
+
 async function readErrorMessage(res: Response): Promise<string> {
 	try {
 		const body = (await res.json()) as { message?: string };
@@ -291,7 +311,7 @@ class PlayerState {
 		else this.playQueue(list, index);
 	}
 
-	addToQueue(item: QueueItem) {
+	playNextItem(item: QueueItem) {
 		this.playNext([item]);
 	}