Handle Unicode decimal input consistently

[codeforester]

Summary

• use str.isdecimal() before integer conversion
• preserve the friendly positive-integer error for superscript and other digit-like input
• cover both accepted decimal digits and rejected superscript input

Closes #145.

Validation

• ruff format --check lib/python/base_cli/history.py tests/test_history.py
• ruff check lib/python/base_cli/history.py tests/test_history.py
• pytest -q tests/test_history.py
• mypy --strict lib/python/base_cli
• git diff --check