Prevent navigation keys from triggering actions during IME composition (#36540)

Fixes  #36532 

Refined the Enter key trigger logic in the repository filter to prevent
actions during IME composition.

By checking the e.isComposing property, the filter now correctly
distinguishes between "confirming an IME candidate" and "submitting the
search." This prevents premature search triggers when users press Enter
to select Chinese/Japanese characters.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/modules/fomantic/dropdown.ts

@@ -225,6 +225,7 @@ function attachDomEvents(dropdown: HTMLElement, focusable: HTMLElement, menu: HT
   };
 
   dropdown.addEventListener('keydown', (e: KeyboardEvent) => {
+    if (e.isComposing) return;
     // here it must use keydown event before dropdown's keyup handler, otherwise there is no Enter event in our keyup handler
     if (e.key === 'Enter') {
       const elItem = menu.querySelector<HTMLElement>(':scope > .item.selected, .menu > .item.selected');