Allow custom/smaller installation in Pi

Thanks for the great work, plannotator is really the best annotation tool I have used so far.

One problem though is that I don't use all the features, for me personally I only use annotate last/file, review, not plan mode/goals etc.

I'm also not sure what the skills are for, the registered command are good enough.

Today I can disable the skills with `pi config` but not other features like plan and goal, is it possible to support this customization?

Some ideas:

- Group the features in different files so users can disable unneeded ones with `pi config`?
- Allow disabling them in plannotator config?

Haven't dig into the details about how feasible are the above but would like to get your opinions first, thanks