Improve config directory detection on Windows and Unix (XDG)

[kamilmac]

Summary

Add Windows support for config directory resolution and ignore unibear.md

Details

• Extend getAppConfigDir() in src/utils/helpers.ts:
  • Check Deno.build.os === "windows".
  • On Windows, use APPDATA or fallback to %HOME%\AppData\Roaming and append unibear.
  • On other platforms, use XDG_CONFIG_HOME or default to ~/.config and append unibear.
• Update .gitignore to exclude unibear.md.

This ensures Unibear stores configs in the correct platform-specific locations.