feat: label AI-generated conversation messages

tests/dashboard/conversations.test.tsx

@@ -40,7 +40,7 @@ function detailFixture(chat = alice) {
   return {
     ...chat,
     messages: [
-      { sender: 'me', text: 'Hello Alice', timestamp: 1_785_999_900_000, isSelf: true },
+      { sender: 'me', text: 'Hello Alice', timestamp: 1_785_999_900_000, isSelf: true, isAi: true },
       { sender: 'alice', text: 'Good to hear from you', timestamp: 1_786_000_000_000, isSelf: false },
     ],
     triggeringPost: {
@@ -136,6 +136,7 @@ describe('ConversationsPage', () => {
       expect(profileLink).toHaveAttribute('href', 'https://www.reddit.com/u/alice');
     }
     expect(screen.getByText('Good to hear from you')).toBeInTheDocument();
+    expect(screen.getByLabelText('Sent by AI')).toHaveTextContent('AI');
     expect(screen.getByRole('link', { name: 'Looking for a chat' })).toHaveAttribute('href', expect.stringContaining('post-1'));
     expect(screen.getByRole('img', { name: 'Source post: Looking for a chat' })).toHaveAttribute(
       'src',