feat!: upgrade to SvelteKit 3 and adapter-bun

- run sv migrate sveltekit-3: config moves into vite.config.ts, $lib becomes
  #lib, $env/dynamic becomes $app/env/private via src/env.ts, $app/environment
  becomes $app/env, hook types move to @sveltejs/kit/hooks
- env vars stay optional (the migrator defaulted them to ''), and BANCHO_MODE,
  which it missed, is declared and passed to simulatorEnabled
- handleError only logs and masks unknown errors; Kit 3 now routes 404s and
  error(...) through it too
- json()/text() become Response.json()/new Response(); goto keepFocus/noScroll
  becomes reset: false; invalidateAll becomes refreshAll; page.url is copied
  before mutating
- replace adapter-node with @sveltejs/adapter-bun; prod-server.ts wraps
  Bun.serve to add native WebSockets (bunSockets) for /ws paths, since the
  generated server has no websocket option
- drop the Kit readdir patch: Kit 3 sorts route entries itself
- match view and broadcast pages use the live score modules

BREAKING CHANGE: requires SvelteKit 3, TypeScript 6 and Bun 1.4; the build
output is build/index.js from adapter-bun, started through prod-server.ts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/components/broadcast/PresetPreview.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
 	import Overlay from './Overlay.svelte';
-	import { demoChannel, demoPayload } from '$lib/broadcast/demo';
-	import type { Layout, SceneId } from '$lib/broadcast/layout';
+	import { demoChannel, demoPayload } from '#lib/broadcast/demo.js';
+	import type { Layout, SceneId } from '#lib/broadcast/layout.js';
 
 	/** A small live render of a layout with the demo match; the checkerboard is where OBS shows through. */
 	const { layout, scene = 'gameplay' }: { layout: Layout; scene?: SceneId } = $props();