Support Cursor OAuth client registration

[sam-tombury]

Relaxes the restriction on redirect_uri during OAuth client registration (and token flows) from AnyHttpUrl to AnyUrl.

Motivation and Context

Cursor uses deeplinks with a custom scheme for redirect_uri when registering OAuth clients for MCP, which currently fails validation (as it is not a valid AnyHttpUrl).

How Has This Been Tested?

Tested an MCP server using this branch and successfully registered Cursor as an OAuth client.

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[asparsh29kumar]

This will actually be really helpful! I just opened an issue for this #897.