feat: Implement Tab/Enter navigation and Cmd+Enter save shortcut

[lornakelly]

Description

Add keyboard navigation to support efficient field editing:

• Tab: Move to next field (Shift+Tab for previous)
• Enter: Finish current field and move to next (does NOT save)

Motivation

Power users need keyboard shortcuts to edit nodes efficiently without reaching for the mouse. The Tab/Enter pattern keeps users in a flow state

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.