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/menus.svelte.ts

@@ -0,0 +1,27 @@
+import {
+	contextMenuStateFor,
+	type ContextMenuState
+} from '$lib/components/TrackContextMenu.svelte';
+import { player } from './player/player.svelte';
+import { queueItemForTarget, type TrackTarget } from './tracks';
+
+export function createTrackMenu() {
+	let state = $state<ContextMenuState | null>(null);
+
+	return {
+		get state() {
+			return state;
+		},
+		open(event: MouseEvent, target: TrackTarget) {
+			state = contextMenuStateFor(event, target);
+		},
+		close() {
+			state = null;
+		},
+		playNext() {
+			if (!state) return;
+			player.playNextItem(queueItemForTarget(state));
+			state = null;
+		}
+	};
+}