Add help on F1 keystroke

[rolandwalker]

Description

• open documentation index in web browser on F1
• emit output using prompt_toolkit methods such that the prompt is restored including pending input
• include the docs URL in the output in case the browser did not open
• include alternate F1 key sequence that prompt_toolkit doesn't handle
• update TIPS and key_bindings.rst

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]

Findings

1. Potential prompt corruption + uncaught exceptions from browser launch
   webbrowser.open_new_tab() is invoked outside run_in_terminal and without error handling. If the browser command writes to stdout/stderr or raises (common on headless systems), this can corrupt the prompt or bubble exceptions into the key handler. Consider wrapping the browser call inside run_in_terminal and catching webbrowser.Error/OSError so F1 never destabilizes the UI.
   File: mycli/key_bindings.py:51 and mycli/key_bindings.py:58

Missing tests / edge cases

1. No coverage for the new F1 behavior
   There are no tests asserting that the F1 binding emits help text and attempts a browser open. A lightweight unit test could monkeypatch webbrowser.open_new_tab and prompt_toolkit.application.run_in_terminal to assert both are called, and that failures don’t raise.
   File: mycli/key_bindings.py:51 and mycli/key_bindings.py:58

If you want, I can sketch a minimal pytest for this.