Architecture audit

Audit a codebase for shallow modules — places where the interface is nearly as complex as the implementation, where understanding one concept requires bouncing between many small files, where pure functions were extracted just for testability but the real bugs hide in how they're called, or where tightly-coupled modules leak across their seams. Surface them as deepening opportunities (refactors that turn shallow modules into deep ones), apply the deletion test, and walk the design tree with the user. Supports parallel sub-agent fanout for 'Design It Twice'-style interface exploration. Use whenever the user wants to improve architecture, find refactoring opportunities, con…