build(deps): upgrade web to SvelteKit 3 and vitest 5

Move the SvelteKit config into vite.config.js, replace the $lib alias with
#lib subpath imports (dropping the vitest alias), extend $app/tsconfig, and
pass asset() paths without a leading slash. Drop the @babel/core and js-yaml
overrides, which no longer match anything in the tree.

web/test/game-engine.test.js

@@ -7,7 +7,7 @@ import {
   loadUnlimitedStats,
   saveUnlimitedStats,
   submitGuess,
-} from "$lib/game-engine";
+} from "#lib/game-engine.js";
 import { AATROX, AHRI } from "./fixtures/champions";
 
 /** Minimal stand-in for compareChampions — the engine only stores what this returns. */