feat: Cross-references tra web-developer e altre skills

Analisi completata:
- Web-developer references rimangono dedicate (tecniche: HTML/CSS/JS)
- Shared references rimangono per UX/design patterns (strategici)

Aggiunti riferimenti incrociati:

1. agency-web-developer:
   - +5 shared references (hero, design, navigation, conversion, layout patterns)
   - Flusso: leggi pattern UX → implementa con technical refs

2. agency-design-system:
   - +3 web-developer refs per handoff tecnico
   - Nota: produce design doc, web-developer implementa codice

3. agency-ux-copy:
   - +design_patterns.md
   - +2 web-developer refs per handoff HTML/CSS
   - Nota: produce copy, web-developer implementa codice

4. agency-seo:
   - +2 web-developer refs per implementazione on-page SEO
   - Nota: produce strategia SEO, web-developer implementa HTML

Flusso chiarito:
- Shared refs = COSA fare (pattern UX/design)
- Web-developer refs = COME codificare (implementazione tecnica)

agency-design-system/SKILL.md

@@ -224,11 +224,20 @@ Traduce la direzione creativa in un design system coerente e riutilizzabile.
 
 ## References
 
+### UX/Design Patterns (Shared)
 - [layout_systems.md](../../references/layout_systems.md) — Grid e spacing
 - [navigation_patterns.md](../../references/navigation_patterns.md) — IA patterns
 - [design_patterns.md](../../references/design_patterns.md) — UI patterns
 - [qa_visual.md](../../references/qa_visual.md) — QA checklist
 
+### Technical Implementation (Handoff)
+**Per handoff a developer o implementazione diretta:**
+- [html_semantics.md](../agency-web-developer/references/html_semantics.md) — Semantic HTML structure
+- [css_layout.md](../agency-web-developer/references/css_layout.md) — Bootstrap/custom CSS implementation
+- [js_interactivity.md](../agency-web-developer/references/js_interactivity.md) — jQuery + GSAP patterns
+
+**Nota:** Questa skill produce design system documentato. Per implementazione codice, consultare agency-web-developer.
+
 ---
 
 ## Note