feature: Allow .claude directory to show up in @ autocompletion

It seems claude code omits dot-prefixed directories from the @ autocompletion, which makes sense as a general approach.

I suggest that .claude is exempt from this and shows up in autocomplete. This directory can be used as a home for ai-specific files which can be referenced during prompts. For example, using a subdirectory to hold specs or PRDs. Or having an examples directory containing references you want to point claude to for how to implement tests files or endpoints or something.

It's still possible to reference these with @, but it would be nice to be able to use autocompletion at least for this directory.

Another fuller solution could be to get rid of the dot prefix ignoring aside from some defaults (like .git), and let users configure which dirs to ignore.