`redirect` should handle non-ASCII characters

Describe the bug

import { redirect } from '@sveltejs/kit';

export const load = () => {
  redirect(303, '/ㄱ');
};

Server-side redirect with Korean characters result in [500] GET / error.

Invalid redirect location "/ㄱ": this string contains characters that cannot be used in HTTP headers

Reproduction

https://github.com/hyunbinseo/svelte-kit-templates/tree/svelte-kit-16054

System Info

System:
  OS: Windows 11 10.0.26200
  CPU: (8) x64 Intel(R) Core(TM) Ultra 7 258V
  Memory: 8.07 GB / 31.48 GB
Binaries:
  Node: 24.16.0 - C:\Users\hyunb\AppData\Local\fnm_multishells\7248_1781599625491\node.EXE
  npm: 11.13.0 - C:\Users\hyunb\AppData\Local\fnm_multishells\7248_1781599625491\npm.CMD
  pnpm: 11.5.1 - C:\Users\hyunb\AppData\Local\fnm_multishells\7248_1781599625491\pnpm.CMD
  Deno: 2.4.0 - C:\Users\hyunb\.deno\bin\deno.EXE
Browsers:
  Chrome: 149.0.7827.103
  Edge: Chromium (149.0.4022.69)
  Firefox: 151.0.4 - C:\Program Files\Mozilla Firefox\firefox.exe
npmPackages:
  @sveltejs/adapter-auto: ^7.0.1 => 7.0.1
  @sveltejs/kit: ^2.63.0 => 2.63.1
  @sveltejs/vite-plugin-svelte: ^7.1.2 => 7.1.2
  svelte: ^5.56.1 => 5.56.1
  vite: ^8.0.16 => 8.0.16

Severity

annoyance

Additional Information

No response

Start with the reproduction linked in the issue and trace the server-side redirect entry point used by redirect(303, '/ㄱ'). Confirm the failure with a non-ASCII location, then add coverage for this case and verify that the request no longer returns a 500 error.