closes #1688 



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## Summary by cubic
Add a “Fix All Errors” button to the chat that collects all error
messages and sends a single request to resolve them. This helps users
fix multiple errors in one step.

- New Features
- Parse dyad-output type=error messages and track count/last index in
DyadMarkdownParser.
- Show FixAllErrorsButton after the last error when there are 2+ errors,
not streaming, and chatId is present.
- Button streams a prompt listing all errors, shows a loading state, and
displays the error count.

<sup>Written for commit b9762955d3b9cecd3b00c9efb478ce599f60e32d.
Summary will update automatically on new commits.</sup>

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