fix(ui): add historical sales link to main sidebar menus

- Add Ventas Históricas link to dashboard, inventory and customers sidebars
- reports.html already had the link

pos/templates/dashboard.html

@@ -148,6 +148,17 @@
           Reportes
         </a>
 
+        <a href="/pos/historical-sales" class="nav-link">
+          <span class="nav-link__icon">
+            <svg width="16" height="16" viewBox="0 0 16 16" fill="none" stroke="currentColor" stroke-width="1.5">
+              <rect x="2" y="3" width="12" height="11" rx="1"/>
+              <path d="M2 6h12" stroke-width="1.2"/>
+              <path d="M5 2v2M11 2v2"/>
+            </svg>
+          </span>
+          Ventas Históricas
+        </a>
+
         <div class="sidebar__section-label">Gestión</div>
 
         <a href="/pos/marketplace" class="nav-link">