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/enhancements/components/custom-amount.css

@@ -356,42 +356,7 @@
 }
 
 /* ============================================================
- * 18. 签到日历可视化
- * ============================================================ */
-.aksrt-signin-calendar__grid {
-    display: grid;
-    grid-template-columns: repeat(7, 1fr);
-    gap: 4px;
-}
-
-.aksrt-signin-calendar__day {
-    aspect-ratio: 1;
-    display: flex;
-    align-items: center;
-    justify-content: center;
-    border-radius: 6px;
-    background: var(--surface-2, #F4F5F7);
-    font-size: 12px;
-    color: var(--color-ink-3);
-    transition: all 0.2s;
-}
-
-.aksrt-signin-calendar__day.is-signed {
-    background: var(--color-success, #10B981);
-    color: #fff;
-}
-
-.aksrt-signin-calendar__day.is-today {
-    border: 2px solid var(--color-primary, var(--color-primary));
-}
-
-.aksrt-signin-calendar__day.is-signed.is-today {
-    background: var(--color-primary, var(--color-primary));
-    border-color: var(--color-primary, var(--color-primary));
-}
-
-/* ============================================================
- * 19. VIP 等级标识
+ * 18. VIP 等级标识
  * ============================================================ */
 .aksrt-vip-badge {
     display: inline-flex;