Create a dedicated interop channel in stan config

[karmaniverous]

Right now, outbound interop messages are written to .stan/interop and inbounds are simply added to imports.

Create a more intentional structure that assumes the same structure in other STAN projects. Example:

stan.config.yml

stan-core:
  interop:
    get-dotenv: ../get-dotenv

Directory structure:

• .stan
• interop
• get-dotenv
• in
  * ... inbound messages
• out
  * ... outbound messages

Refine the system prompt such that "compose an interop message to get-dotenv" will put the right message in the right place, and "review the latest interop message from get-dotenv" will look in the right place.

Make sure all interop message titles are timestamped.