Update docs, skill counts, and UX/setup-engine skills for v0.4.0

- Update skill count to 66 and hook count to 12 across README, skills-reference, and badges
- Add QA & Testing section to README and skills-reference (qa-plan, smoke-check, soak-test, etc.)
- Add Input & Platform section to technical-preferences.md (populated by /setup-engine)
- Document post-compact, notify, and validate-skill-change hooks in hooks-reference
- Expand /setup-engine, /ux-design, /ux-review, /design-system skills with input/platform context
- Restructure workflow-catalog: move UX steps into pre-production phase, improve descriptions
- Expand UPGRADING.md and WORKFLOW-GUIDE.md with v0.4.0 guidance
- Add skill-flow-diagrams examples and CODEOWNERS

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/skills/design-system/SKILL.md

@@ -457,6 +457,16 @@ For **Visual/Audio**: Coordinate with `art-director` and `audio-director` if det
 is needed. Often a brief note suffices at the GDD stage.
 
 For **UI Requirements**: Coordinate with `ux-designer` for complex UI systems.
+After writing this section, check whether it contains real content (not just
+`[To be designed]` or a note that this system has no UI). If it does have real
+UI requirements, output this flag immediately:
+
+> **📌 UX Flag — [System Name]**: This system has UI requirements. In Phase 4
+> (Pre-Production), run `/ux-design` to create a UX spec for each screen or
+> HUD element this system contributes to **before** writing epics. Stories that
+> reference UI should cite `design/ux/[screen].md`, not the GDD directly.
+>
+> Note this in the systems index for this system if you update it.
 
 For **Open Questions**: Capture anything that came up during design that wasn't
 fully resolved. Each question should have an owner and target resolution date.