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/reports.html

@@ -105,6 +105,12 @@
           </svg>
           <span>Clientes</span>
         </a>
+        <a href="/pos/workshop" class="nav-item">
+          <svg class="nav-item__icon" viewBox="0 0 18 18" fill="none" stroke="currentColor" stroke-width="1.5">
+            <path d="M11 4.7a.8.8 0 0 0 0 1.1l1.2 1.2a.8.8 0 0 0 1.1 0l2.8-2.8a4.5 4.5 0 0 1-6 6l-5.2 5.2a1.6 1.6 0 0 1-2.2-2.2l5.2-5.2a4.5 4.5 0 0 1 6-6L11 4.7z"/>
+          </svg>
+          <span>Taller</span>
+        </a>
 
         <a href="/pos/invoicing" class="nav-item">
           <svg class="nav-item__icon" viewBox="0 0 18 18" fill="none" stroke="currentColor" stroke-width="1.5">