feat(ticket): record urges in thread, show urge count in admin, mail admins

- aksrt_ticket gains urge_count / last_urge_time (schema 3.1.0)
- cooldown moves from transient to an atomic conditional UPDATE
- urge inserts a system reply rendered as a centered notice (not quotable)
- admin list badge + info card row for urge count / last time
- new ticket_urge_admin mail event via aksrt_ticket_urged

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/css/admin/tickets.css

@@ -156,6 +156,28 @@
 .aksrt-ticket-detail__reply { margin: 0; }
 .aksrt-ticket-detail__reply.is-admin { margin-left: 32px; background: #f0f6fc; border-color: #c5d9ed; }
 .aksrt-ticket-detail__reply.is-user { margin-right: 32px; }
+/* 系统记录（催单等）：居中细条，与对话气泡区分。 */
+.aksrt-ticket-detail__system {
+	display: flex;
+	justify-content: center;
+	gap: 8px;
+	margin: 0;
+	color: var(--aksrt-tk-muted);
+	font-size: 12px;
+}
+.aksrt-ticket-detail__system span { color: #b32d2e; }
+/* 催单徽标：列表标题旁 + 详情信息卡。 */
+.aksrt-ticket-urge {
+	display: inline-block;
+	padding: 0 6px;
+	color: #b32d2e;
+	font-size: 12px;
+	line-height: 18px;
+	background: #fcf0f1;
+	border: 1px solid #f0c3c5;
+	border-radius: 9px;
+	vertical-align: middle;
+}
 .aksrt-ticket-detail__quote {
 	margin: 0 0 8px;
 	padding: 6px 10px;