Setup Storybook

[lornakelly]

Summary

 Set up Storybook for the project and create a minimal web application entry that initializes and renders the Diagram Editor component, enabling isolated UI development and interactive documentation.

Goals

 * Enable isolated development of the Diagram Editor via Storybook.
 * Make Storybook the primary documentation for MVP.
 * Allow contributors to visually test diagram changes without backend integration.

Non-Goals

 * Full documentation site generation beyond Storybook.
 * Complex theming support (dark/light toggle can come later).
 * Full workflow parsing or SDK integration (static/mock data is acceptable for now).

Description

 This issue establishes Storybook as the isolated development and documentation environment for the Diagram Editor component.

 * Install and configure Storybook for React + TypeScript.
 * Ensure compatibility with Webpack configuration.
 * Add at least one story
 * Add npm scripts:

   * pnpm run start - run stotybook in dev mode
   * pnpm run build:storybook - build storybook static content for publishing

 Storybook should act as:

 * Interactive documentation
 * Primary showcase mechanism for MVP features