fix(core): ensure new chat when entering chat page (#13146)

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

## Summary by CodeRabbit

* **New Features**
* Added an option to always start a new AI chat session instead of
reusing the latest one.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/core/src/desktop/pages/workspace/chat/index.tsx

@@ -82,6 +82,7 @@ export const Component = () => {
       const sessionId = await client.createSession({
         workspaceId,
         promptName: 'Chat With AFFiNE AI' satisfies PromptKey,
+        reuseLatestChat: false,
         ...options,
       });