FASE 7: Quick Wins de Performance — Optimización Fase 1

Cambios implementados:

1. Nginx:
   - gzip on (compresión JS/CSS/JSON)
   - Cache headers para assets estáticos (6M)
   - Proxy buffer tuning (10s connect, 30s read)

2. Frontend catalog.js:
   - Reemplazados 8x innerHTML += en loops por map+join
   - Event delegation en breadcrumb y cart (elimina memory leak)
   - AbortController en apiFetch (evita race conditions)
   - sessionStorage cache para years-all y brands por modo

3. Frontend templates HTML:
   - defer en todos los scripts POS (mejora First Paint)

4. Dashboard JS:
   - innerHTML += fix en dashboard.js y cuentas.js

5. Base de datos:
   - Índice parcial idx_wi_part_stock_positive en warehouse_inventory

6. Documentación:
   - docs/performance_audit_2026.md con análisis completo y roadmap

Tests: 73/73 pasando (compat + fase3 + fase5 + fase6)

pos/templates/invoicing.html

@@ -2386,12 +2386,12 @@
     </div>
   </div>
 
-  <script src="/pos/static/js/i18n.js"></script>
-  <script src="/pos/static/js/app-init.js"></script>
-  <script src="/pos/static/js/pos-utils.js"></script>
-  <script src="/pos/static/js/sidebar.js"></script>
-  <script src="/pos/static/js/invoicing.js"></script>
-  <script src="/pos/static/js/sync-engine.js"></script>
+  <script src="/pos/static/js/i18n.js" defer></script>
+  <script src="/pos/static/js/app-init.js" defer></script>
+  <script src="/pos/static/js/pos-utils.js" defer></script>
+  <script src="/pos/static/js/sidebar.js" defer></script>
+  <script src="/pos/static/js/invoicing.js" defer></script>
+  <script src="/pos/static/js/sync-engine.js" defer></script>
   <script>if('serviceWorker' in navigator){navigator.serviceWorker.register('/pos/sw.js',{scope:'/pos/'});}</script>
 
 </body>