Fixes #249.

Summary

• render application help for bare --help and -h invocations instead of command help for the default list command
• update the global help option description used in command/application help output
• refresh shell completion fixtures and add a news fragment

Tests

• PYTHONPATH=src python -m pytest tests\test_application.py tests\commands\completion\test_completions_command.py -q
• python -m ruff check src\cleo\application.py tests\test_application.py
• python -m ruff format --check src\cleo\application.py tests\test_application.py
• python -m towncrier check --compare-with origin/main