Fortitude should respect .gitignore

[LiamPattinson]

Ruff has the options --respect-gitignore (active by default) and --no-respect-gitignore. If running under the latter, ruff check . at the top level of a git repo will start looking into folders like build/, target/, etc (it seems to avoid searching under venv/.venv unless you specifically request them).

Fortitude should behave similarly.

[LiamPattinson]

A complication to this is that there may be nested .gitignore files, so we'll have to add to the set of excluded file patterns as we recurse through directories. It'll probably be best to see how Ruff handles this.