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/UsersWechatTemplate.css

@@ -1 +0,0 @@
-.aksrt-wechat__status[data-v-cb377b9c]{display:grid;grid-template-columns:repeat(auto-fit,minmax(200px,1fr));gap:16px;margin-bottom:24px}.aksrt-wechat__status-card[data-v-cb377b9c]{display:flex;align-items:center;gap:12px;padding:16px;background:#fff;border-radius:8px;border:1px solid #e8e8e8}.aksrt-wechat__status-icon[data-v-cb377b9c]{width:40px;height:40px;border-radius:8px;display:flex;align-items:center;justify-content:center;font-size:16px}.aksrt-wechat__status-icon--ok[data-v-cb377b9c]{background:#d4edda;color:#155724}.aksrt-wechat__status-icon--warn[data-v-cb377b9c]{background:#fff3cd;color:#856404}.aksrt-wechat__status-icon--info[data-v-cb377b9c]{background:#d1ecf1;color:#0c5460}.aksrt-wechat__status-value[data-v-cb377b9c]{font-size:18px;font-weight:600;color:#1a1a2e}.aksrt-wechat__status-label[data-v-cb377b9c]{font-size:12px;color:#888}.aksrt-wechat__form-card[data-v-cb377b9c]{background:#fff;border:1px solid #e8e8e8;border-radius:8px;padding:24px;margin-bottom:16px}.aksrt-wechat__form-card h3[data-v-cb377b9c]{margin:0 0 16px;font-size:16px;font-weight:600}.aksrt-form-hint[data-v-cb377b9c]{font-size:12px;color:#888;margin-top:4px}