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/TerminalTabs.tsx

@@ -96,7 +96,8 @@ export function TerminalTabs({
   // Handle key events during editing
   const handleKeyDown = useCallback(
     (e: React.KeyboardEvent) => {
-      if (e.key === 'Enter') {
+      // Skip if composing (e.g., Japanese IME input)
+      if (e.key === 'Enter' && !e.nativeEvent.isComposing) {
         e.preventDefault()
         submitEdit()
       } else if (e.key === 'Escape') {