close #1870 





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## Summary by cubic
Adds a “Copy” button to error banners and chat error output so users can
quickly copy error messages with clear feedback. Addresses Linear #1870.

- **New Features**
- Introduced CopyErrorMessage component that writes to clipboard and
shows “Copied” for 2s.
- Added the copy button to the Preview error banner and DyadOutput;
actions grouped at the bottom beside “Fix with AI”.
- Added Playwright e2e test and helpers to verify copy behavior and
clipboard content.

<sup>Written for commit 12e9bf1437ded36dc022e1d795025580d2ffd111.
Summary will update automatically on new commits.</sup>

<!-- End of auto-generated description by cubic. -->