Adding a button for copying error messages (#1882)

close #1870 





<!-- This is an auto-generated description by cubic. -->
---
## 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. -->

e2e-tests/helpers/test_helper.ts

@@ -575,6 +575,13 @@ export class PageObject {
     await this.page.getByRole("button", { name: "Fix error with AI" }).click();
   }
 
+  async clickCopyErrorMessage() {
+    await this.page.getByRole("button", { name: /Copy/ }).click();
+  }
+
+  async getClipboardText(): Promise<string> {
+    return await this.page.evaluate(() => navigator.clipboard.readText());
+  }
   async clickFixAllErrors() {
     await this.page.getByRole("button", { name: /Fix All Errors/ }).click();
   }