Support for global .clang-format file

[Bix3]

If a user has no .clang-format file in the worktree but one in the home dir for example then clang format is not ran in the current state.

https://github.com/anomalyco/opencode/blob/a7cae8f674071a103db0c254ff01dbec19111e8a/packages/opencode/src/format/formatter.ts#L157

[github-actions[bot]]

This issue might be a duplicate of existing issues. Please check:

• #1482: opencode ran my code through an auto-formatter? - Users experiencing unexpected auto-formatting when no config is present
• #8387: On file edit it is also formatted - Related to unwanted formatting during edits

Feel free to ignore if none of these address your specific case.