Telescope agent CLI --uploadUrl argument doesn't work with telescopetest.io/upload endpoint

## Describe the bug

The telescope agent just got a new CLI argument `--uploadUrl` to upload the results via API to an arbitrary endpoint, but this doesn't work with https://telescopetest.io/api/upload. Attempts return a 403 error, which telescopetest-io shouldn't be returning anywhere.

We'll probably need to test with telescopetest-io locally, and then check if the error comes from Astro/Cloudflare deployment, etc.

## Telescope info

Please include the following information about your environment:

**Telescope version**: f714b464e5a82b069badd9689ebd30f307e0c217, basically just the build right after #146
**Node version**: v24.13.1
**Operating system version**: macOS 26.3

## Steps to reproduce

Tried running `npx . -u https://www.cloudflare.com/ -b chrome --uploadUrl https://telescopetest.io/api/upload`.

## Expected results

Expected to see the upload succeed and see the result on https://telescopetest.io/results

## Observed results

Console output from the command:
```
api info => browserContext.newCDPSession started
api info <= browserContext.newCDPSession succeeded
api info => browserContext.setOffline started
api info <= browserContext.setOffline succeeded
api info => browserContext.close started
api info <= browserContext.close succeeded
Error uploading zip file: 403 Forbidden
Test ID:2026_02_23_14_10_42_ae492587-acce-4f87-8047-80dcd4a39db5
```