feat: Fase 1-3 completas - precios proveedor, multi-sucursal, factura global

Fase 1: Lista de precios de proveedor
- Tabla supplier_catalog_prices en master DB
- Endpoints GET/POST/PUT/DELETE /supplier-catalog/prices
- Upload CSV/Excel de precios de proveedor
- Visualizacion de supplier_price en catalogo y POS

Fase 2: Multi-sucursal completo
- Migracion v4.0: inventory.branch_id=NULL, tabla inventory_stock
- Campos fiscales en branches (RFC, regimen, CP, serie CFDI, certificados)
- Trigger trg_update_inventory_stock para sincronizar stock por sucursal
- Backend config_bp.py con CRUD de sucursales fiscales
- Backend inventory_bp.py y pos_bp.py refactorizados para inventario compartido
- Backend invoicing_bp.py usa datos fiscales de la sucursal de la venta
- Frontend config.html/js con modal de sucursales expandido

Fase 3: Factura global mensual
- Migracion v4.1: tablas global_invoice_sales, sales.global_invoiced_at
- build_global_invoice_xml() con InformacionGlobal SAT-compliant
- Servicio global_invoice.py para agrupar ventas PUE <=000
- Endpoints POST/GET /global-invoice y /global-invoice/eligible-sales
- Frontend invoicing.html/js con boton y modal de factura global

pos/services/inventory_engine.py

@@ -25,22 +25,23 @@ def _safe_g(attr, default=None):
 def get_stock(conn, inventory_id, branch_id=None):
     """Get current stock for an inventory item. Optionally filter by branch.
 
-    Uses Redis cache first, then inventory_stock_summary, falls back to
-    PostgreSQL SUM query.
+    Uses Redis cache first, then inventory_stock (per-branch) or
+    inventory_stock_summary (total), falls back to PostgreSQL SUM query.
     """
     # Try Redis first
     cached = get_cached_stock(inventory_id, branch_id)
     if cached is not None:
         return cached
 
-    # Use inventory_stock_summary (O(1) lookup)
     cur = conn.cursor()
     if branch_id:
+        # Per-branch stock from inventory_stock
         cur.execute(
-            "SELECT stock FROM inventory_stock_summary WHERE inventory_id = %s AND branch_id = %s",
+            "SELECT stock FROM inventory_stock WHERE inventory_id = %s AND branch_id = %s",
             (inventory_id, branch_id)
         )
     else:
+        # Total stock from inventory_stock_summary
         cur.execute(
             "SELECT stock FROM inventory_stock_summary WHERE inventory_id = %s",
             (inventory_id,)
@@ -73,13 +74,14 @@ def get_stock(conn, inventory_id, branch_id=None):
 def get_stock_bulk(conn, branch_id=None):
     """Get stock for all items. Returns dict {inventory_id: stock_quantity}.
 
-    Uses inventory_stock_summary for O(1) bulk lookup.
+    Uses inventory_stock (per-branch) or inventory_stock_summary (total)
+    for O(1) bulk lookup.
     """
     cur = conn.cursor()
     if branch_id:
         cur.execute("""
             SELECT inventory_id, stock
-            FROM inventory_stock_summary WHERE branch_id = %s
+            FROM inventory_stock WHERE branch_id = %s
         """, (branch_id,))
     else:
         cur.execute("""