feat(tickets): make ticket title/content/reply length limits configurable

Add ticket_title_max / ticket_content_max / ticket_reply_max to the
users/ticket schema (PHP + SPA) with clamped TicketSettings readers.
All write paths (front REST, admin REST, note REST, native admin page)
and front-end maxlength/counters now read the configured limits.
Remove the hardcoded TICKET_CONTENT_MAX constant.

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

assets/js/ticket-center-core.js

@@ -35,6 +35,12 @@
     return parseInt(settings().attachmentMax, 10) || 5;
   }
 
+  /** 字数上限（后台「工单中心 → 提交设置」配置，PHP 侧已夹取边界）。 */
+  function lengthMax(kind) {
+    var defaults = { title: 200, content: 5000, reply: 3000 };
+    return parseInt(settings()[kind + 'Max'], 10) || defaults[kind];
+  }
+
   function escapeHtml(value) {
     return String(value === null || value === undefined ? '' : value)
       .replace(/&/g, '&')
@@ -359,6 +365,7 @@
     settings: settings,
     attachmentEnabled: attachmentEnabled,
     attachmentMax: attachmentMax,
+    lengthMax: lengthMax,
     escapeHtml: escapeHtml,
     notyf: notyf,
     request: request,