fix: Prevent accidental message submission during IME composition

Add isComposing check to prevent Enter key from submitting messages
while Japanese (or other) IME input is in progress.

Affected components:
- AssistantChat
- ExpandProjectChat
- SpecCreationChat
- FolderBrowser
- TerminalTabs

ui/src/components/ExpandProjectChat.tsx

@@ -88,7 +88,8 @@ export function ExpandProjectChat({
   }
 
   const handleKeyDown = (e: React.KeyboardEvent) => {
-    if (e.key === 'Enter' && !e.shiftKey) {
+    // Skip if composing (e.g., Japanese IME input)
+    if (e.key === 'Enter' && !e.shiftKey && !e.nativeEvent.isComposing) {
       e.preventDefault()
       handleSendMessage()
     }