Annotator (#1861)

<!-- This is an auto-generated description by cubic. -->
## Summary by cubic
Adds an in-app screenshot annotator to the Preview panel for Pro users
so you can capture the current app view, draw or add text, and submit an
annotated image to chat.

- **New Features**
- Pen button in PreviewIframe to toggle annotator; captures a screenshot
via worker messaging and displays it in a Konva canvas.
- Tools: select, freehand draw, and draggable text; supports undo/redo,
delete, and resizing with Transformer. Canvas scales to the container.
Includes a color picker.
- Submit exports a PNG and attaches it to the chat via useAttachments;
prefills the chat input; annotator auto-closes after submit.
  - Pro-only: non-Pro users see an upsell screen.
- State atoms added: annotatorModeAtom, screenshotDataUrlAtom,
attachmentsAtom; PreviewIframe now handles dyad-screenshot-response
messages.

- **Dependencies**
  - Added konva, react-konva, perfect-freehand, and html-to-image.
- Proxy now injects html-to-image and the new dyad-screenshot-client.js
for screenshot capture.

<sup>Written for commit 580aca271c5993a0dc7426e36e34393e073bd67b.
Summary will update automatically on new commits.</sup>

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

e2e-tests/helpers/test_helper.ts

@@ -553,6 +553,22 @@ export class PageObject {
     await this.page.getByTestId("preview-open-browser-button").click();
   }
 
+  async clickPreviewAnnotatorButton() {
+    await this.page
+      .getByTestId("preview-annotator-button")
+      .click({ timeout: Timeout.EXTRA_LONG });
+  }
+
+  async waitForAnnotatorMode() {
+    // Wait for the annotator toolbar to be visible
+    await expect(this.page.getByRole("button", { name: "Select" })).toBeVisible(
+      { timeout: Timeout.MEDIUM },
+    );
+  }
+
+  async clickAnnotatorSubmit() {
+    await this.page.getByRole("button", { name: "Add to Chat" }).click();
+  }
   locateLoadingAppPreview() {
     return this.page.getByText("Preparing app preview...");
   }