add opencode agent and cleanup dropdown

[Light2Dark]

📝 Summary

Fixes #7340
I cleaned up the dropdown for selecting a new session, but not the main panel. I think we can do that when we add another model. Seems okay now

Used this command to run ACP: npx stdio-to-ws "npx opencode-ai acp" --port 3023
However, there seems to be an issue where the response is received many times
(edit: fixed by modifying the handleResumeSession code)

🔍 Description of Changes

📋 Checklist

• I have read the contributor guidelines.
• For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on Discord, or the community discussions (Please provide a link if applicable).
• I have added tests for the changes made.
• I have run the code and verified that it works as expected.

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Project	Deployment	Preview	Comments	Updated (UTC)
marimo-docs	Ready	Preview	Comment	Dec 2, 2025 5:55pm

[Light2Dark]

I'm thinking we can add a beta tag, because this agent edits files without requesting permission.
And needs --watch flag

[mscolnick]

nice cleanup!

[mscolnick]

I'm thinking we can add a beta tag, because this agent edits files without requesting permission. And needs --watch flag

I'm open to adding this. They all have their own quirks as well, but maybe opencode more than others