Add web_url to add_branch MCP tool response

Summary

The add_branch MCP tool (!248453 (merged)) was reimplemented to wrap the existing Mutations::Repositories::Branches::Create GraphQL mutation instead of calling Branches::CreateService directly. This dropped the web_url field from the tool's response, because Types::BranchType only exposes name and commit.

Proposal

Add a web_url field to Types::BranchType (or otherwise surface it in the add_branch tool response) so that Mcp::Tools::Repositories::Branches::AddBranchTool can include it again, matching the original tool design.

References

• !248453 (merged) (introduced add_branch, dropped web_url in favor of reusing the GraphQL mutation)