feat(pos/workshop): add lightweight workshop/taller module

- Add DB migration v4.4_workshop.sql (sale_id, service_catalog,
  reserved_quantity, SO_RESERVE/SO_RELEASE operation types).
- Extend service_order_engine with inventory reservation, release,
  convert-to-sale, mechanic assignment, and service catalog CRUD.
- Extend service_order_bp with /reserve, /convert-to-sale,
  /assign-mechanic, and /service-catalog endpoints.
- Create workshop Kanban UI: workshop.html, workshop.js, workshop.css.
- Add /pos/workshop route and sidebar navigation (sidebar.js + inline
  templates).
- Add 11 unit tests with mocked cursors.
- Update FASES_IMPLEMENTADAS.md with FASE 9 documentation.

Tests: 92 passing (61 console + 20 Facturapi + 11 workshop).

pos/templates/invoicing.html

@@ -118,6 +118,12 @@
           </svg>
           <span>Clientes</span>
         </a>
+        <a class="nav-item" href="/pos/workshop">
+          <svg class="nav-item__icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round">
+            <path d="M14.7 6.3a1 1 0 0 0 0 1.4l1.6 1.6a1 1 0 0 0 1.4 0l3.77-3.77a6 6 0 0 1-7.94 7.94l-6.91 6.91a2.12 2.12 0 0 1-3-3l6.91-6.91a6 6 0 0 1 7.94-7.94l-3.76 3.76z"/>
+          </svg>
+          <span>Taller</span>
+        </a>
 
         <a class="nav-item is-active" href="/pos/invoicing" aria-current="page">
           <svg class="nav-item__icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round">