fix(inventory): soft-delete suppliers via HTML delete route

Match the behaviour of the API v1 endpoint by marking the supplier as
inactive instead of hard-deleting it. This preserves referential
integrity with purchase orders, stock items and audit data and removes
the "cannot delete supplier with associated stock items" failure mode.

app/routes/inventory.py

@@ -1747,26 +1747,25 @@ def edit_supplier(supplier_id):
 @login_required
 @admin_or_permission_required("manage_suppliers")
 def delete_supplier(supplier_id):
-    """Delete supplier"""
+    """Delete (deactivate) supplier.
+
+    Performs a soft delete by setting ``is_active=False`` so historical
+    purchase orders, stock items and audit data referencing the supplier
+    remain intact. Matches the behaviour of the API v1 endpoint.
+    """
     supplier = Supplier.query.get_or_404(supplier_id)
 
-    # Check if supplier has associated stock items
-    item_count = SupplierStockItem.query.filter_by(supplier_id=supplier_id).count()
-
-    if item_count > 0:
-        flash(_("Cannot delete supplier with associated stock items. Remove items first."), "error")
-        return redirect(url_for("inventory.view_supplier", supplier_id=supplier_id))
-
     try:
         code = supplier.code
-        db.session.delete(supplier)
+        supplier.is_active = False
+        supplier.updated_at = datetime.utcnow()
         safe_commit()
 
         log_event("supplier_deleted", supplier_code=code)
-        flash(_("Supplier deleted successfully."), "success")
+        flash(_("Supplier deactivated successfully."), "success")
     except Exception as e:
         db.session.rollback()
-        flash(_("Error deleting supplier: %(error)s", error=str(e)), "error")
+        flash(_("Error deactivating supplier: %(error)s", error=str(e)), "error")
 
     return redirect(url_for("inventory.list_suppliers"))