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/AssistantChat.tsx

@@ -134,7 +134,8 @@ export function AssistantChat({
   }
 
   const handleKeyDown = (e: React.KeyboardEvent<HTMLTextAreaElement>) => {
-    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()
       handleSend()
     }

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()
     }

ui/src/components/FolderBrowser.tsx

@@ -269,7 +269,8 @@ export function FolderBrowser({ onSelect, onCancel, initialPath }: FolderBrowser
                     className="flex-1"
                     autoFocus
                     onKeyDown={(e) => {
-                      if (e.key === 'Enter') handleCreateFolder()
+                      // Skip if composing (e.g., Japanese IME input)
+                      if (e.key === 'Enter' && !e.nativeEvent.isComposing) handleCreateFolder()
                       if (e.key === 'Escape') {
                         setIsCreatingFolder(false)
                         setNewFolderName('')

ui/src/components/SpecCreationChat.tsx

@@ -127,7 +127,8 @@ export function SpecCreationChat({
   }
 
   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()
     }

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') {