Implementing the planned copperhead explain stretch command

[AyushVUpadhye]

Hi! I was reading the technical specification and noticed that copperhead explain <refdes|net|pin> is already listed as a planned stretch command.

I couldn't find an open issue or an implementation for it, so I wanted to check whether this is something you'd be open to accepting as a contribution.

My idea is to implement a focused first version that provides deterministic schematic lookup:

• copperhead explain U1 → component metadata, pins, and connected nets
• copperhead explain GND → all pins connected to the net
• copperhead explain R2.1 → the net connected to the specified pin

This implementation would:

• be read-only,
• require no LLM,
• support --json,
• reuse the existing schematic query functionality where possible.

The higher-level "why is R7 here?" behavior described in the specification could be implemented in a later iteration by incorporating documentation and design rationale.

Does this scope align with the roadmap? If so, I'd be happy to work on it.