Allow OAuth client registration without a client name

[lazerg]

RFC 7591 §2 lists client_name as an OPTIONAL field for Dynamic Client Registration, but OAuthRegisterController rejects any registration that omits both client_name and the legacy name, returning 400 invalid_client_metadata. This blocks spec-compliant clients — notably Claude's remote MCP connector, whose registration request leaves out client_name and currently fails with "Couldn't register with … sign-in service".

This PR makes client_name/name optional. When neither is supplied, the client name falls back to the host of the first redirect URI (e.g. example.com), and to MCP Client when no host can be derived. The existing client_name > name precedence is unchanged, so requests that already send a name behave exactly as before.

Tests are updated to cover a registration request without a name and the fallback behaviour.

Fixes #253

[lazerg]

cc @pushpak1300 — since you built the OAuth/DCR layer in #233, this is likely your area. Small change to make client_name optional per RFC 7591 §2, which lets Claude's remote connector register (its DCR request omits client_name). Tests, Pint, PHPStan (level 8) and Rector all pass locally; CI is just waiting on the first-time-contributor approval. Thanks for taking a look!

[taylorotwell]

Thanks for your pull request to Laravel!

I appreciate you taking the time to submit this; however, it appears this contribution may have been primarily AI-generated without careful human review and consideration.

We've found that AI-generated code often doesn't align well with Laravel's conventions, architectural decisions, and the specific context of what we're trying to accomplish with the framework. Quality contributions require thoughtful human insight into the codebase.

If you're interested in contributing to Laravel, I'd encourage you to familiarize yourself with the existing codebase, engage with the community, and submit PRs that reflect your own understanding and careful consideration of the problem you're solving.

[pushpak1300]

Thanks.