feat(brand): add brand sort order and drag-to-reorder

Add a sort_order column to brands with a migration, expose a
PUT /api/tenant/brands/order reorder endpoint, and wire the
admin-web BrandsView with drag-and-drop reordering plus i18n.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/tenant/domain/brand.go

@@ -9,6 +9,7 @@ type Brand struct {
 	Website     *string
 	Description *string
 	Status      string
+	SortOrder   int
 	CreatedAt   time.Time
 	UpdatedAt   time.Time
 }