[BUG] Claude Code Web GitHub proxy blocks binary attachment uploads

Description

I'm trying to use Claude Code Web sessions to autonomously create E2E tests, run them, record a video of the test execution, and attach that video to the resulting GitHub PR.

GitHub now supports uploading attachments using:

POST https://uploads.github.com/user-attachments/assets
Content-Type: application/octet-stream

The uploaded URL can then be included in the PR description or a comment.

However, this doesn't work from Claude Code Web because GitHub requests go through Anthropic's proxy, which appears to require JSON request bodies.

The upload fails with:

415
Request bodies must declare Content-Type: application/json.

The request never reaches GitHub.

Expected behavior

Claude Code Web should allow binary uploads to GitHub's attachment endpoint, so agents can attach artifacts generated during a session to PRs or comments.

For example:

1. Claude implements an E2E test.
2. Claude runs the test and records a video.
3. Claude uploads the .mp4 to GitHub.
4. Claude embeds the resulting attachment URL in the PR description.

This isn't limited to videos. It would also enable agents to attach screenshots, images, logs, and other artifacts generated while working on a PR.

Why this is useful

For autonomous coding sessions, generated artifacts are often part of verifying the work. Being able to include screenshots or test recordings directly in the PR makes it much easier for reviewers to understand and verify the changes without requiring a separate upload step outside Claude Code Web.

Reproduction

A request like:

curl -X POST \
  "https://uploads.github.com/user-attachments/assets?name=test.mp4&content_type=video/mp4&repository_id=<REPO_ID>" \
  -H "Content-Type: application/octet-stream" \
  --data-binary @test.mp4

fails in Claude Code Web with:

415 Request bodies must declare Content-Type: application/json.

The same GitHub attachment flow works outside Claude Code Web.

It would be great if the GitHub proxy could allow binary request bodies for uploads.github.com/user-attachments/assets.