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/ToolsHealth.css

@@ -1 +0,0 @@
-.aksrt-health-grid[data-v-485f9fd2]{display:grid;grid-template-columns:repeat(auto-fit,minmax(240px,1fr));gap:16px}