[Feature Request] Add configurable plan file output directory and custom plan templates

Question

**Bug Description**
It would be nice to have a way to specify where clause writes plan files. I often have claude write a plan, then I go in and add comments starting with `>`  (or fix an issue myself, sometimes). It would be nice if I could direct claude to write the plans in the project folder (`${my_project}/.claude/plans`) as that would make it easier to access via my ide. It would also be nice if I could modify the template claude uses for plans as I have project specific requirements that