feat(forum): plate follow cash coupons + free auto-order

- Meta _aksrt_follow_pay_coupon_s + plate admin toggle (money only)
- Plate_Follow_Pay soft/hard coupon apply, free-after-discount, burn via shared helper
- Cashier auto-submits free topic/plate orders; topic coupon label no longer "预留"

assets/js/cms-download.js

@@ -448,7 +448,7 @@
 			window.location.reload();
 			return;
 		}
-		// Free VIP topic/plate_follow still need a free-order unlock POST; content free can reload.
+		// Content free: reload. Topic/plate free: auto free-order POST (VIP free / free-after-coupon).
 		if (preview.is_free && preview.pay_type !== 'topic' && preview.pay_type !== 'plate_follow') {
 			window.location.reload();
 			return;
@@ -458,6 +458,25 @@
 		const priceType = (preview._price_type || preview.price_type || '');
 		const apiKind = preview._api_kind
 			|| (preview.pay_type === 'topic' ? 'topic' : (preview.pay_type === 'plate_follow' ? 'plate_follow' : 'content'));
+
+		// Auto-submit free topic/plate orders so user doesn't click through empty cash UI.
+		if (preview.is_free && (apiKind === 'topic' || apiKind === 'plate_follow') && !isPoints) {
+			open(
+				'<h3 class="aksrt-dl-modal__title">' + tt('confirm_buy', '确认购买') + '</h3>' +
+				'<p class="aksrt-dl-modal__msg">' + tt('processing', '处理中…') + '</p>',
+				returnFocusEl
+			);
+			const freeBtn = document.createElement('button');
+			freeBtn.type = 'button';
+			freeBtn.style.display = 'none';
+			freeBtn.setAttribute('data-price-type', priceType || '');
+			document.body.appendChild(freeBtn);
+			const freeCode = String(preview.coupon_code || preview._coupon_code || '');
+			submitPurchase(preview.post_id, 'cash', 'balance', freeBtn, returnFocusEl, freeCode, apiKind);
+			try { freeBtn.remove(); } catch (e0) { /* ignore */ }
+			return;
+		}
+
 		let amountLabel = escapeHtml(preview.amount_label || '');
 		let baseLabel = escapeHtml(preview.base_label || '');
 		const listLabel = escapeHtml(preview.list_amount_label || preview.amount_label || amountLabel);