fix: use stable initialMessages for useChat

[codeincontext]

Description

I've been finding that the frontend has been getting in a render loop that calls getChat constantly. @JBR90 worked out that #459 was probably the PR that introduced it

I've found that initialMessages was different on each render, which might cause useChat to reload and trigger another tRPC request

I've also been finding that the AI SDK calls like append aren't stable. This doesn't seem to completely fix that, though changing initialMessages could be the cause

This PR fixes the feedback loop, though it will still be calling a little too much

Issue(s)

Fixes #

How to test

1. Open the chat page for an existing lesson plan
2. Look at the console

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Name	Status	Preview	Comments	Updated (UTC)
oak-ai-lesson-assistant	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 16, 2025 5:23pm

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Playwright test results

 17 passed
 2 skipped

Details

 Open report ↗︎
 19 tests across 16 suites
 2 minutes, 30 seconds
 cc1db58

Skipped tests

No persona › tests/auth.test.ts › authenticate through Clerk UI
No persona › tests/chat-performance.test.ts › Component renders during lesson chat › There are no unnecessary rerenders across left and right side of chat

[oak-machine-user]

🎉 This PR is included in version 1.22.0 🎉

The release is available on GitHub release

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