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. -->

src/atoms/chatAtoms.ts

@@ -1,4 +1,4 @@
-import type { Message } from "@/ipc/ipc_types";
+import type { FileAttachment, Message } from "@/ipc/ipc_types";
 import { atom } from "jotai";
 import type { ChatSummary } from "@/lib/schemas";
 
@@ -20,3 +20,5 @@ export const chatsLoadingAtom = atom<boolean>(false);
 // Used for scrolling to the bottom of the chat messages (per chat)
 export const chatStreamCountByIdAtom = atom<Map<number, number>>(new Map());
 export const recentStreamChatIdsAtom = atom<Set<number>>(new Set<number>());
+
+export const attachmentsAtom = atom<FileAttachment[]>([]);

src/atoms/previewAtoms.ts

@@ -15,6 +15,9 @@ export const currentComponentCoordinatesAtom = atom<{
 
 export const previewIframeRefAtom = atom<HTMLIFrameElement | null>(null);
 
+export const annotatorModeAtom = atom<boolean>(false);
+
+export const screenshotDataUrlAtom = atom<string | null>(null);
 export const pendingVisualChangesAtom = atom<Map<string, VisualEditingChange>>(
   new Map(),
 );