Forward Vercel callbacks from web origin

[arseniycodes]

Summary

• Forward /vercel/oauth/callback requests that land on the web origin to the API callback origin.
• Preserve the full Vercel OAuth query string so the existing callback handler can exchange the code and complete setup.

Validation

• pnpm exec tsx --test src/oauthCallbackForwarding.test.ts in apps/web
• pnpm --filter @superlog/web typecheck

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Summary by cubic

Forward Vercel OAuth callbacks that land on the web app to the API callback endpoint, preserving the full query string. Prevents failed setup when users are redirected to the web domain.

• Bug Fixes
  • Forward /vercel/oauth/callback from web origin to the API origin with the original query string.
  • Added a client-side forwarder component and integrated it into App to redirect on load.
  • Added unit tests for forwarding behavior and non-matching paths.

^{Written for commit 63c4638. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}