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/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;