fix: clamp teleported dropdown position to viewport bounds

When neither upward nor downward direction has enough space for the
full menu height, clamp the position so the menu stays within the
viewport instead of overflowing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/renderer/extensions/vueNodes/widgets/components/form/dropdown/FormDropdown.vue

@@ -178,11 +178,10 @@ function toggleDropdown() {
       spaceBelow < MENU_HEIGHT_WITH_GAP && spaceAbove > spaceBelow
 
     if (shouldTeleport) {
-      if (openUpward.value && rect.top < MENU_HEIGHT_WITH_GAP) {
-        openUpward.value = false
-      }
       fixedPosition.value = {
-        top: openUpward.value ? rect.top : rect.bottom,
+        top: openUpward.value
+          ? Math.max(MENU_HEIGHT_WITH_GAP, rect.top)
+          : Math.min(rect.bottom, window.innerHeight - MENU_HEIGHT_WITH_GAP),
         left: Math.min(rect.right, window.innerWidth - MENU_WIDTH)
       }
     }