feat(KB-626): add mobile responsive styles for model dropdown

- Add media query for tablet screens (max-width: 768px) with 70vh max-height
- Add media query for mobile screens (max-width: 640px) with 60vh max-height
- Center dropdown horizontally using transform translateX
- Set responsive width with viewport calculation and min-width unset

packages/dashboard/app/styles.css

@@ -5364,6 +5364,26 @@ body {
   font-style: italic;
 }
 
+/* Mobile responsive model dropdown */
+@media (max-width: 768px) {
+  .model-combobox-dropdown {
+    max-height: 70vh;
+    max-height: 70dvh; /* Use dynamic viewport height where supported */
+  }
+}
+
+@media (max-width: 640px) {
+  .model-combobox-dropdown {
+    max-height: 60vh;
+    max-height: 60dvh;
+    /* Ensure dropdown doesn't overflow horizontally on small screens */
+    left: 50%;
+    transform: translateX(-50%);
+    width: calc(100vw - 32px);
+    min-width: unset;
+  }
+}
+
 /* ============================================================
    THEME SYSTEM
    ============================================================ */