fix: handle invalid CLI path inputs gracefully

[Kcstring]

Summary

• guard CLI file path resolution and directory checks against OSError
• surface invalid path inputs via tool_error and exit with status 1 instead of crashing
• add a regression test covering an overlong path input

Testing

• python3 -m pytest tests/basic/test_main.py -k invalid_long_path
• python3 -m pytest tests/basic/test_main.py -k "empty_dir_no_files_on_command or emptqy_dir_new_file or dname_and_fname"
• python3 -m ruff check aider/main.py tests/basic/test_main.py

Fixes #5082