fix(core): ai image upload failed (#13405)

Close [AI-407](https://linear.app/affine-design/issue/AI-407)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Ensured that images included in the chat context are now properly sent
as attachments during AI chat interactions.

* **Tests**
* Enhanced chat tests to verify that the AI correctly identifies images
of kittens or cats in its responses.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

tests/affine-cloud-copilot/e2e/chat-with/image.spec.ts

@@ -36,6 +36,12 @@ test.describe('AIChatWith/Image', () => {
         status: 'success',
       },
     ]);
+
+    const { content } = await utils.chatPanel.getLatestAssistantMessage(page);
+    await expect(
+      content.toLowerCase().includes('kitten') ||
+        content.toLowerCase().includes('cat')
+    ).toBe(true);
   });
 
   test('support chat with mutiple images', async ({