fix: parse git remote arguments safely

[EvanProgramming]

Fixes #52

Parse git_remote arguments with shlex and validate the supported empty-list, add name URL, and remove name forms before invoking Git. URLs retain punctuation and successful add/remove operations report deterministic results.

Validation:

• ./venv/bin/python -m unittest tests.test_tools -v (real temporary Git repository add/list/remove)
• make check
• make lint
• make test (127 tests)
• git diff --check
• PR head 1e6c1e4 is GPG-signed and GitHub verified.