fix(checkin): keep modal runtime shell fullscreen with modal-mini class

Trigger classes are applied to the fixed shell; .modal-mini's
width:400px + auto margins collapsed the shell (and its backdrop)
into a centered column. Neutralize dialog-only width classes on the
shell so the fullscreen backdrop covers the viewport again.

assets/css/frontend/modal-runtime.css

@@ -39,6 +39,17 @@ body.aksrt-modal-runtime-open {
   overflow: hidden;
 }
 
+/* ---- 对话框宽度类不得作用于壳 ----
+   触发器沿用参考主题的 data-class 语义（modal-mini/full-sm 等），
+   但这些类落在 fixed 全屏壳上时，.modal-mini 的 width:400px +
+   auto 边距会把壳压成居中单列，蒙版随之只覆盖一列。 */
+.aksrt-modal-runtime.modal-mini,
+.aksrt-modal-runtime.full-sm {
+  width: auto;
+  max-width: none;
+  margin: 0;
+}
+
 /* ---- modal runtime shell ---- */
 .aksrt-modal-runtime {
   position: fixed;