lev-builder: POC → Formalize → Migrate

Core principle: Build in a workspace POC, prove it works, migrate to ~/lev canonical paths.

Why This Exists

PROBLEM:
- Work happens across mixed workspaces (project-local, workshop, plugins)
- BD issues are in lev (lev-* prefix)
- Need to know WHERE to put things in Leviathan
- Need prior art check before creating new

SOLUTION:
- lev-builder orchestrates the full workflow
- POC in `~/lev/workshop/poc` (or project-local skills) → migrate to `~/lev/core` when proven
- Uses graph operations for decisioning, then applies explicit filesystem patches during migration