adding a button for fixing all errors (#1785)

closes #1688 



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

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

e2e-tests/helpers/test_helper.ts

@@ -575,6 +575,10 @@ export class PageObject {
     await this.page.getByRole("button", { name: "Fix error with AI" }).click();
   }
 
+  async clickFixAllErrors() {
+    await this.page.getByRole("button", { name: /Fix All Errors/ }).click();
+  }
+
   async snapshotPreviewErrorBanner() {
     await expect(this.locatePreviewErrorBanner()).toMatchAriaSnapshot({
       timeout: Timeout.LONG,