Motivation for the change, related issues

When using blueprints that reference private GitHub repositories, the OAuth authentication flow has several issues:

1. Hash blueprints are lost: URL fragments (e.g., #{"steps":...}) are not sent to servers in HTTP requests, so they're lost during the OAuth redirect to GitHub and back.

2. Token not used after OAuth: The createGitAuthHeaders() function captured the OAuth token at creation time, but the token is only available after the OAuth redirect completes. It still works here because the page reloads after OAuth, and the token is acquired before boot starts on the fresh page. The bug would only show when we remove the blueprint parameters as we do in personal-wp.

1. User loads page with private repo blueprint
2. Boot fails with GitAuthenticationError (no token)
3. Auth modal shown, user authenticates
4. GitHub redirects back with ?code=...
5. Page loads fresh - acquireOAuthTokenIfNeeded() runs at module import time
6. Token is exchanged and stored before React renders
7. Boot starts, createGitAuthHeaders() is called - token already exists
8. Blueprint succeeds

3. Client setup runs after errors: When startPlaygroundWeb throws an error (e.g., GitAuthenticationError), the catch block handles it but execution continues to run client setup code, which shouldn't happen for failed boots.

Implementation details

1. Add buildOAuthRedirectUrl(): Converts URL fragment blueprints to blueprint-url query parameters before the OAuth redirect, preserving the blueprint through the round-trip.

2. Fix token capture timing: Move token retrieval inside the returned function so it's captured at call time, not creation time.

3. Add early return in catch block: Prevent client setup code from running after boot errors.

Testing Instructions (or ideally a Blueprint)

1. Navigate to the Playground with a hash blueprint referencing a private GitHub repo:

   https://playground.wordpress.net/#{"steps":[{"step":"installPlugin","pluginData":{"resource":"url","url":"https://github.com/user/private-repo/archive/refs/heads/main.zip"}}]}
   

2. Observe the GitHub auth modal appears
3. Click "Connect your GitHub account" and complete the OAuth flow
4. After redirect, verify the blueprint is preserved and applied with authentication