fix: startNewChat now always creates new session

- Changed startNewChat to async and always create a new session
- No longer depends on currentSession existing

src/views/SearchView.vue

@@ -711,12 +711,13 @@ function newChat() {
   localStorage.removeItem(SESSION_STORAGE_KEY)
 }
 
-function startNewChat() {
+async function startNewChat() {
   newChat()
   showHistory.value = false
-  // Create new session if there's a current session
-  if (currentSession.value) {
-    handleNewSession()
+  // Always create a new session
+  const newSession = await createSession('未命名搜尋', mode.value)
+  if (newSession) {
+    setCurrentSession(newSession)
   }
 }