fix: add Load Example button and fix example file download (#11)

[colorbank]

Problem

Fixes #11

The "example circuit json file" link pointed to the GitHub blob viewer URL (/blob/main/assets/...) which:

1. Doesn't trigger a file download
2. Just navigates to GitHub's file preview page

Solution

Two changes in src/App.tsx:

1. Added a "Load Example" button in the upload section — fetches the example JSON from the raw GitHub URL and loads it directly into the Circuit JSON Viewer with one click. No manual download/upload needed.

2. Fixed the footer download link — changed from GitHub blob URL to the raw GitHub URL with download="usb-c-flashlight.json" attribute, so clicking it actually downloads the file.

Testing

• Click "Load Example" → USB-C flashlight circuit loads directly into the viewer ✅
• Click "Download example circuit json file" → file downloads to disk ✅

/claim #11

[vercel]

@colorbank is attempting to deploy a commit to the tscircuit Team on Vercel.

A member of the Team first needs to authorize it.

[colorbank]

Quick unblock request: this PR is ready from the code side, but the only failing status is Vercel authorization.

Current status:

• GitHub checks/statuses show Vercel failing with Authorization required to deploy.
• Local verification: npx --yes bun@latest run build passes on the PR branch.
• The PR is still mergeable with no reported code/test check failure.

Could a tscircuit team member please authorize the Vercel deployment so the status check can proceed? Thank you!