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>

tests/widget-system/ticket-schema-contract.test.cjs

@@ -26,6 +26,9 @@ const FIELD_ORDER = [
   'ticket_attachment_max',
   'ticket_order_link_s',
   'ticket_urge_interval',
+  'ticket_title_max',
+  'ticket_content_max',
+  'ticket_reply_max',
 ];
 
 const GROUPS = [
@@ -128,6 +131,11 @@ test('TicketSettings falls back to schema defaults and clamps numerics', () => {
   assert.match(body, /max\(1, min\(9, \(int\)/);
   assert.match(body, /max\(1, min\(1440, \(int\)/);
 
+  // 字数上限：标题 10..200（VARCHAR(200)），描述 / 回复 100..16000（TEXT 65535 字节 / utf8mb4）。
+  assert.match(body, /max\(10, min\(200, \(int\) \(self::all\(\)\['ticket_title_max'\] \?\? 200\)\)\)/);
+  assert.match(body, /max\(100, min\(16000, \(int\) \(self::all\(\)\['ticket_content_max'\] \?\? 5000\)\)\)/);
+  assert.match(body, /max\(100, min\(16000, \(int\) \(self::all\(\)\['ticket_reply_max'\] \?\? 3000\)\)\)/);
+
   // 公告文案走 kses（后台允许 HTML）。
   assert.match(body, /wp_kses_post/);
   // 分区名与 schema key 一致（常量在 all() 之前声明，故对整份文件断言）。