`create_branch` branch tool fails with generic message when rule is violated oppose to the Github UI

[emilk-port]

Describe the bug

create_branch branch tool fails with generic message when rule is violated oppose to the Github UI

Affected version

github-mcp-server/remote-639e169e86264c0ee9704f141ec6bc5615266486

Steps to reproduce the behavior

1. set rule for branch naming
2. try to create an invalid branch name from the UI -> see detailed error about the rules violation

3. try to create the same branch name from mcp -> see generic 422 error

Expected vs actual behavior

expecting to see the same errors like we see in the website, and in general more descriptive errors
detailed errors helps the LLM to recover from failed tool calls

[quseijuro-design]

Thanks for the report. Would maintainers accept a small PR that preserves GitHub's structured validation message (subject to existing redaction conventions) instead of returning a generic 422, with a regression test for a branch-naming rule violation? I would keep the scope limited to create_branch and leave successful behavior unchanged. Is there a preferred error format or existing abstraction to use?