fix: prevent mobile slot field overlap

Stack weekday and date controls on narrow screens and constrain native select
widths to their grid column.

.commitmessage

@@ -1,4 +1,4 @@
-feat: add mobile slot configuration
+fix: prevent mobile slot field overlap
 
-Replace the mobile table with a searchable card editor while retaining the
-desktop table. Add a mobile-friendly date picker layout and sticky save action.
+Stack weekday and date controls on narrow screens and constrain native select
+widths to their grid column.

src/components/MobileConfigList.css

@@ -146,6 +146,7 @@
   .mobile-config-card__core-fields select,
   .mobile-config-card__range {
     box-sizing: border-box;
+    width: 100%;
     min-height: 2.6rem;
     border: 1px solid #cbd5e1;
     border-radius: 5px;
@@ -251,6 +252,12 @@
     font-weight: 600;
   }
 
+  @media (max-width: 420px) {
+    .mobile-config-card__core-fields {
+      grid-template-columns: 1fr;
+    }
+  }
+
   .desktop-config-table,
   .desktop-config-actions {
     display: none;