feat: add ChatEmptyState component and integrate it into ChatMessageList for improved user experience

src/stores/chat.ts

@@ -675,6 +675,7 @@ async function deleteSession(sessionKey: string): Promise<void> {
 
   if (state.currentSessionKey === sessionKey) {
     const nextSession = remaining[0]?.key ?? getDefaultMainSessionKey();
+    const hasRemainingSessions = remaining.length > 0;
     patchState({
       ...basePatch,
       currentSessionKey: nextSession,
@@ -688,7 +689,7 @@ async function deleteSession(sessionKey: string): Promise<void> {
       lastUserMessageAt: null,
     });
 
-    if (nextSession) {
+    if (hasRemainingSessions && nextSession) {
       await loadHistory(nextSession);
     }
     return;