OPCIÓN A: A2 Virtual Scroll + A3 Celery + A4 asyncpg PoC + A5 particionamiento

A2 — Virtual scroll en tablas grandes:
- Nuevo helper VirtualScroll en pos/static/js/virtual-scroll.js
- inventory.js: tabla de productos con virtual scroll
- customers.js: tabla de clientes con virtual scroll
- fleet.js: renderMaintenance() y renderHistory() con virtual scroll
- Templates envueltos en .vs-container para scroll

A3 — Celery worker queue:
- pos/celery_app.py + pos/tasks.py (warm cache, bulk import, reports)
- Blueprint tasks_bp.py con endpoints /pos/api/tasks/*
- Script scripts/start_celery.sh

A4 — asyncpg + Quart PoC:
- pos/async_catalog.py: endpoint /pos/api/catalog/async-search
- scripts/benchmark_async_catalog.py: benchmark Flask vs Quart

A5 — Particionar vehicle_parts:
- scripts/partition_vehicle_parts.py: migración segura por hash (16 particiones)
- Soporta --dry-run, --skip-swap, --skip-drop

Tests: 36/36 pasando

pos/templates/inventory.html

@@ -312,25 +312,27 @@
           </div>
 
           <div class="table-wrapper">
-            <table class="data-table" id="stockTable">
-              <thead>
-                <tr>
-                  <th>Barcode</th>
-                  <th>No. Parte</th>
-                  <th>Nombre</th>
-                  <th>Marca</th>
-                  <th style="text-align:right">Stock</th>
-                  <th style="text-align:right">Costo</th>
-                  <th style="text-align:right">Precio 1</th>
-                  <th style="text-align:right">Precio 2</th>
-                  <th style="text-align:right">Precio 3</th>
-                  <th>Ubicación</th>
-                  <th>Acciones</th>
-                </tr>
-              </thead>
-              <tbody id="productTableBody">
-              </tbody>
-            </table>
+            <div class="vs-container" style="max-height:60vh;overflow-y:auto;">
+              <table class="data-table" id="stockTable">
+                <thead>
+                  <tr>
+                    <th>Barcode</th>
+                    <th>No. Parte</th>
+                    <th>Nombre</th>
+                    <th>Marca</th>
+                    <th style="text-align:right">Stock</th>
+                    <th style="text-align:right">Costo</th>
+                    <th style="text-align:right">Precio 1</th>
+                    <th style="text-align:right">Precio 2</th>
+                    <th style="text-align:right">Precio 3</th>
+                    <th>Ubicación</th>
+                    <th>Acciones</th>
+                  </tr>
+                </thead>
+                <tbody id="productTableBody">
+                </tbody>
+              </table>
+            </div>
             <div class="table-footer">
               <div id="productPagination"></div>
             </div>
@@ -811,6 +813,7 @@
   <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/virtual-scroll.js" defer></script>
   <script src="/pos/static/js/inventory.js" defer></script>
   <script src="/pos/static/js/offline-banner.js" defer></script>
   <script src="/pos/static/js/sync-engine.js" defer></script>