Navigating to an API handler route 404's in logs.

Describe the bug

Navigating to an API only route yields a 404 in the console. If we do a redirect inside the api route to the app, it does not update the URL correctly.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-ipxflmtx

1. Open dev console
2. Click the red link
3. Witness error in console
4. Observe URL bar is not at the correct route (/moonlight)

Logs

Error: Not found: /out_there
    SvelteKitError control.js:45
    navigate client.js:1312
    _start_router client.js:2175
    _start_router client.js:2066
    start client.js:314
    async* (index):212
    promise callback* (index):211
.localservice@runtime.c8c182a3.js:26:94631
    error .localservice@runtime.c8c182a3.js:26
    handleError app.js:18
    handle_error client.js:1642
    navigate client.js:1312
    _start_router client.js:2175
    _start_router client.js:2066
    start client.js:314
    <anonymous> (index):212
    (Async: promise callback)
    <anonymous> 

### System Info

```Shell
npx envinfo --system --binaries --browsers --npmPackages "{svelte,@sveltejs/*,vite}"
Need to install the following packages:
envinfo@7.14.0
Ok to proceed? (y) 
 
  System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.20.3 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @sveltejs/adapter-auto: ^3.3.1 => 3.3.1 
    @sveltejs/kit: ^2.12.1 => 2.12.1 
    svelte: ^5.14.4 => 5.14.4 
    vite: ^6.0.3 => 6.0.3 

### Severity

blocking all usage of SvelteKit

Start with the linked StackBlitz reproduction and follow the failing navigation in the console, especially the client.js navigate/_start_router and control.js locations shown in the log. Trace the API-only route redirect behavior and verify that visiting the route no longer logs a 404 and that the browser URL becomes /moonlight.