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/inventory.html

@@ -149,6 +149,16 @@
           <span>Reportes</span>
         </a>
 
+        <a class="nav-item" href="/pos/historical-sales">
+          <svg class="nav-item__icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round">
+            <rect x="4" y="5" width="16" height="16" rx="1"/>
+            <line x1="4" y1="10" x2="20" y2="10"/>
+            <line x1="8" y1="3" x2="8" y2="5"/>
+            <line x1="16" y1="3" x2="16" y2="5"/>
+          </svg>
+          <span>Ventas Históricas</span>
+        </a>
+
         <div class="nav-section-label">Sistema</div>
 
         <a class="nav-item" href="/pos/config">