write-adr - capture an architecture decision

An ADR (Architecture Decision Record) is a short markdown file that explains:

• The context that made the decision necessary.
• The decision itself.
• The alternatives considered and why they lost.
• The consequences - what's better, what's worse, what's now harder.

Good ADRs answer "why did we do X instead of Y?" months later, when the person who knew has left or forgotten.

This skill discovers the repo's existing ADR convention, discusses the decision with the user, then writes the ADR matching the local format.

Phase 0 - Find existing ADRs