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/async_catalog.py

@@ -0,0 +1,93 @@
+"""Async catalog search PoC using Quart + asyncpg.
+
+Run:
+    hypercorn async_catalog:app --bind 0.0.0.0:5002
+
+Endpoint:
+    GET /pos/api/catalog/async-search?q=filtro&limit=50&tenant_id=1
+
+This demonstrates I/O non-blocking search using asyncpg.
+"""
+
+import os
+import asyncio
+import asyncpg
+from quart import Quart, request, jsonify, g
+
+app = Quart(__name__)
+
+MASTER_DB_URL = os.environ.get('MASTER_DB_URL', 'postgresql://postgres@/nexus_autoparts')
+
+# Shared connection pool
+_pool = None
+
+async def _get_pool():
+    global _pool
+    if _pool is None:
+        _pool = await asyncpg.create_pool(MASTER_DB_URL, min_size=2, max_size=10)
+    return _pool
+
+
+@app.before_serving
+async def startup():
+    await _get_pool()
+
+
+@app.after_serving
+async def shutdown():
+    global _pool
+    if _pool:
+        await _pool.close()
+        _pool = None
+
+
+@app.route('/pos/api/catalog/async-search')
+async def async_search():
+    q = request.args.get('q', '').strip()
+    if not q or len(q) < 2:
+        return jsonify({'data': []})
+    limit = min(request.args.get('limit', 50, type=int), 100)
+
+    pool = await _get_pool()
+    async with pool.acquire() as conn:
+        # Simple text search (PoC scope)
+        clean_q = q.upper().replace(' ', '')
+        rows = await conn.fetch("""
+            SELECT p.id_part, p.oem_part_number, p.name_part, p.name_es,
+                   p.image_url, p.group_id
+            FROM parts p
+            WHERE REPLACE(UPPER(p.oem_part_number), ' ', '') LIKE $1
+               OR p.name_part ILIKE $2
+               OR p.name_es ILIKE $2
+            ORDER BY p.oem_part_number
+            LIMIT $3
+        """, f'%{clean_q}%', f'%{q}%', limit)
+
+        part_ids = [r['id_part'] for r in rows]
+        vehicle_map = {}
+        if part_ids:
+            vrows = await conn.fetch("""
+                SELECT part_id, name_brand, name_model, year_car
+                FROM part_vehicle_preview
+                WHERE part_id = ANY($1)
+            """, part_ids)
+            for vr in vrows:
+                vehicle_map[vr['part_id']] = f"{vr['name_brand']} {vr['name_model']} {vr['year_car']}"
+
+    results = []
+    for r in rows:
+        results.append({
+            'id': r['id_part'],
+            'oem_part_number': r['oem_part_number'],
+            'name': r['name_part'],
+            'name_es': r['name_es'],
+            'image_url': r['image_url'],
+            'group_id': r['group_id'],
+            'vehicle_info': vehicle_map.get(r['id_part'], ''),
+        })
+
+    return jsonify({'data': results})
+
+
+if __name__ == '__main__':
+    app.run(host='0.0.0.0', port=5002)