feat(checkin): open reference-parity details modal from signed buttons

- Rebuild checkin details modal HTML 1:1 with reference theme:
  colorful header c-blue, user card (points/level), daily reward
  card and 7-day continuous mini cards
- Signed entry buttons (header dropdown, user-card badge, user
  center) become clickable checkin-details-link modal triggers
  instead of disabled buttons
- Swap data-signin-btn to details link in place after successful
  signin (reference .initiate-checkin replacement behavior)
- Add aksrt-checkin-details-modal runtime shell (modal-mini 400px)
- Remove dead code: legacy lite modal, admin-ajax details handler,
  /signin/history route, signin calendar; rebuild public bundles
- Update contract tests to the new checkin modal contract

assets/css/frontend/header-userbox.css

@@ -327,10 +327,8 @@
 }
 
 /* 已签到态对齐参考主题：保留原配色（参考主题签到后仍为同一彩色按钮），
- * 仅禁用指针交互；此前的灰底灰字覆盖是与参考主题的偏差。 */
-.aksrt-header-checkin.is-done,
+ * 且按钮可点击（打开签到详情弹窗）；仅请求进行中的禁用态降不透明度。 */
 .aksrt-header-checkin:disabled,
-.aksrt-header-checkin.is-done:hover,
 .aksrt-header-checkin:disabled:hover {
   cursor: default;
   opacity: .85;