fix(build): remove Sentry upload postbuild hook

[56wj]

Summary

Remove the root postbuild hook so bun run build remains a build-only command and does not attempt a Sentry release or sourcemap upload.

The explicit bun run sentry:sourcemaps command is unchanged for release workflows that have the required credentials and artifact path.

Closes #1444.

Verification

• Parsed package.json with Node.js successfully.
• Ran git diff --check successfully.

The local workspace does not have Bun installed, so the repository build command was not run here.