feat(editor): board shell with iframe frame and selection overlay

React Flow board (pan/zoom + frame drag are pure editor-side transforms
— zero canvas-protocol traffic, <16ms budget) hosting one iframe frame
node on the adapter origin. The frame waits for runtime.ready
(queue-drain) behind an explicit 'Starting preview…' skeleton, then
requests a single Element via render-frame (core-runner-protocol
schema) plus geometry; agent-reported geometry stays frame-local and
click reports drive store selection. The selection ring renders as an
editor-side overlay from reported geometry — chrome never inside the
customer's document (ADR-028). Stories + jsdom component tests for
board/frame/overlay; Storybook stories glob extended to
packages/editor (verified via static build).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

apps/storybook/.storybook/main.ts

@@ -2,7 +2,10 @@ import type { StorybookConfig } from "@storybook/react-vite";
 
 const config: StorybookConfig = {
   framework: "@storybook/react-vite",
-  stories: ["../../../packages/core-ui/src/**/*.stories.@(ts|tsx)"],
+  stories: [
+    "../../../packages/core-ui/src/**/*.stories.@(ts|tsx)",
+    "../../../packages/editor/src/**/*.stories.@(ts|tsx)",
+  ],
   addons: ["@storybook/addon-essentials"],
   docs: {
     autodocs: "tag",