fix: chat loses conversation context between messages

Remove revalidatePath('/chat') from createConversation — it caused
the server to re-render the /chat page after each new conversation,
which reset the useChat hook state and created a new conversation
for every message instead of continuing the existing one.

Sidebar now refreshes client-side after streaming completes.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/app/actions/chat-actions.ts

@@ -21,7 +21,6 @@ export async function createConversation(title: string, notebookId?: string) {
     },
   })
 
-  revalidatePath('/chat')
   return { id: conversation.id, title: conversation.title }
 }
 
@@ -69,6 +68,5 @@ export async function deleteConversation(id: string) {
     where: { id, userId: session.user.id }
   })
 
-  revalidatePath('/chat')
   return { success: true }
 }