perf(web-player): cut down the searches the explore page fires

Typing in the search box navigated on every pause, so single letters and
round-trips back to the same term each triggered a full YouTube search and a
new grid of covers. The debounce is longer, a term identical to the current
one no longer navigates, YouTube is only queried past a minimum length, and
the infinite scroll waits until the sentinel is closer before pulling a page.

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

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import LoaderCircle from '@lucide/svelte/icons/loader-circle';
+	import { INFINITE_SCROLL_ROOT_MARGIN } from '$lib/config';
 
 	interface Props {
 		onLoadMore: () => void;
@@ -8,7 +9,7 @@
 		rootMargin?: string;
 	}
 
-	let { onLoadMore, hasMore, loading, rootMargin = '600px' }: Props = $props();
+	let { onLoadMore, hasMore, loading, rootMargin = INFINITE_SCROLL_ROOT_MARGIN }: Props = $props();
 
 	let sentinel = $state<HTMLDivElement>();
 	let visible = $state(false);

web-player/src/lib/config.ts

@@ -1,3 +1,6 @@
 export const EXPLORE_PAGE_SIZE = 27;
+export const SEARCH_DEBOUNCE_MS = 450;
+export const SEARCH_MIN_LENGTH = 2;
+export const INFINITE_SCROLL_ROOT_MARGIN = '300px';
 export const HOME_LATEST_PAGE_SIZE = 12;
 export const YOUTUBE_FILLER_LIMIT = 27;