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/transport/router.go

@@ -235,6 +235,7 @@ func RegisterRoutes(app *bootstrap.App) {
 	brands.GET("", brandHandler.List)
 	brands.GET("/library-summary", brandHandler.Summary)
 	brands.POST("", brandHandler.Create)
+	brands.PUT("/order", brandHandler.Reorder)
 	brands.GET("/:id", brandHandler.Detail)
 	brands.PUT("/:id", brandHandler.Update)
 	brands.DELETE("/:id", brandHandler.Delete)