feat: include non-repo files for completing /read (take 2, exclude .files)

[jbellis]

This should be faster, but I don't have a repo large enough to reproduce the slowdown in the original version (Cassandra isn't big enough), happy to test against a different repo if you have one in mind.

[paul-gauthier]

Enumerating all the files is just going to be slow for large filesystems.

The main branch has an implementation of this now. Let me know if it works for you.

aider --install-main-branch

[jbellis]

Looks great, thanks!