Add \bug command

[rolandwalker]

Description

Add \bug command, which opens a browser to the GitHub Issues page.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

Review summary
Small, clear change. I see one correctness edge case and one missing test.

Findings (ordered by severity)

1. Misleading success message if browser fails to open. webbrowser.open_new_tab() returns True/False and can raise in some environments, but file_bug always reports success. Consider checking the return value and catching exceptions to show a failure status.
   File: mycli/packages/special/main.py

2. Missing test for the new side effect. There’s no test to assert the command calls the browser opener and handles failure. A unit test that mocks webbrowser.open_new_tab would prevent accidental regressions and avoid opening a browser during tests.
   File: mycli/packages/special/main.py

Open questions / assumptions

• Should \bug be a no-op (with a message) in non-interactive contexts or CI? If yes, guard with a TTY check before opening a browser.

If you want, I can draft the test and error handling changes.

[rolandwalker]

Merging this minor PR without review to help with rebasing. Comments welcome.