🐛 fix: improve dropdown submenu scrolling for tag move functionality

- Set max-height to min(300px, 80vh) for dropdown submenus
- Add media query for small height devices (≤600px) to use 30vh
- Ensures scrollable list when moving topics to tags with many assistants
- Fixes issue where some tags cannot be displayed in move-to dropdown

Fixes #10877

src/renderer/src/assets/styles/ant.css

@@ -102,13 +102,19 @@
 }
 
 .ant-dropdown-menu .ant-dropdown-menu-sub {
-  max-height: 80vh;
+  max-height: min(300px, 80vh);
   width: max-content;
   overflow-y: auto;
   overflow-x: hidden;
   border: 0.5px solid var(--color-border);
 }
 
+@media (max-height: 600px) {
+  .ant-dropdown-menu .ant-dropdown-menu-sub {
+    max-height: 30vh;
+  }
+}
+
 .ant-dropdown {
   background-color: var(--ant-color-bg-elevated);
   overflow: hidden;