feat: more ignore files.

[Kile-Asmussen]

There are several kinds of ignore files besides .gitignore in use:

• .ignore (respected by ripgrep and many others)
• .rignore (ripgrep)
• .aiignore .geminiignore .cursorignore .claudeignore .aiexclude (various AI systems)
• .vscodeignore .codeiumignore (editors)
• .dockerignore (docker)
• etc.

My proposal is to add at least one new flag:

• --ignore-file which takes a list of file names and parses each with the format of a .gitignore file.

And maybe also:

• --all-ignore which just searches up any filename of the format .*ignore and uses those.

Given that --git-ignore already exists, this should not be an overly difficult feature to implement.