chore(admin): stop tracking SPA build; add native product meta box

Remove assets/admin/build from version control (local build only going
forward). Add AKSRT_Product_Meta_Box so product price/stock/shipping/after-
sale fields can be edited on the native aksrt_product edit screen without
the SPA product drawer.

assets/admin/build/ToolsImportExport.css

@@ -1 +0,0 @@
-.aksrt-tools-output[data-v-9ee419ed]{margin:0;padding:14px;border-radius:12px;background:#101828;color:#d0d7e2;font-size:12px;line-height:1.7;white-space:pre-wrap;word-break:break-word}.aksrt-tools-hint[data-v-9ee419ed]{margin:12px 0 0;color:#667085;font-size:12px;line-height:1.7}