chore(skills): add design quality review phase to ship command

[chaliy]

What

Adds Phase 3d (Design Quality Review) to the /ship skill, inserting it between Security Review (3c) and Smoke Testing (4).

Why

This is a greenfield project where clean design matters more than compatibility. The new phase catches shortcuts, lazy abstractions, and premature compromises before they ship — enforcing 8 specific review checkpoints covering abstraction quality, type safety, error design, and module boundaries.

How

Added a new markdown section to .claude/commands/ship.md with 8 review criteria:

1. No shortcut abstractions
2. No lazy wrappers
3. Right abstraction level
4. No stringly-typed interfaces
5. No premature generics
6. No compatibility shims
7. First-class error types
8. Module boundaries enforce invariants

Tests

• Documentation-only change, no code tests needed
• just pre-pr passes (fmt, clippy, all tests green)