feat: Create/update Storybook Stories for Node Editing

[lornakelly]

Description

Add new stories to the existing Features/Diagram-Editor section that specifically demonstrate editing functionality:

1. Editing Mode Stories - New stories with isReadOnly: false showing editable state
2. Field Editing Demo - Interactive story showing field editing with all task types (can be multiple stories)

Why this approach:

• Users can still toggle isReadOnly in Controls panel for any story
• Dedicated editing stories provide focused examples
• Maintains consistency with existing story organisation

Motivation

Dedicated editing stories make development easier by providing isolated environments to build and test editing features. They serve as living documentation for the │
│ editing system, support design review, and enable visual regression testing.

Proposed Implementation

No response

Definition of Done

• Implementation: Fully implemented according to the Open Workflow spec.
• Unit Tests: Comprehensive unit tests are included and passing.
• Integration Tests: Verified within the monorepo and target environments (Web/VS Code).
• Documentation: Updated README.md, ADRs, or official docs.
• Performance: No significant regression in editor responsiveness.
• Accessibility: UI changes comply with accessibility standards.