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/champion-data.test.js

@@ -1,11 +1,12 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
-import { getChampionImageUrl, getTodaySeed } from "$lib/champion-data";
+import { getChampionImageUrl, getTodaySeed } from "#lib/champion-data.js";
 import { AATROX, CHAMPIONS } from "./fixtures/champions";
 
 // $app/paths is a SvelteKit build-time construct with no meaning to a bare
 // Vitest run. Base-path behaviour is verified by the production preview check,
-// not here, so the identity stub is the honest unit-test substitute.
-vi.mock("$app/paths", () => ({ asset: (p) => p }));
+// not here, so the stub mirrors asset() with an empty base: it takes a path
+// without a leading slash and returns it root-relative.
+vi.mock("$app/paths", () => ({ asset: (p) => `/${p}` }));
 
 /**
  * `champions` is module-private with no reset export, so each group gets a fresh
@@ -19,7 +20,7 @@ async function freshModule({ champions = CHAMPIONS, ok = true, status = 200 } =
     json: async () => champions,
   }));
   vi.stubGlobal("fetch", fetchMock);
-  const mod = await import("$lib/champion-data");
+  const mod = await import("#lib/champion-data.js");
   return { mod, fetchMock };
 }
 

web/test/classic-mode.test.js

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { CLASSIC_ATTRIBUTES, compareChampions } from "$lib/classic-mode";
+import { CLASSIC_ATTRIBUTES, compareChampions } from "#lib/classic-mode.js";
 import { AATROX, AHRI, AKALI, BELVETH } from "./fixtures/champions";
 
 /** Pull one attribute's comparison out of the 7-entry result array. */

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. */