feat: Replace diagram editor modal with full screen

[lornakelly]

Description

Replaces the diagram editor modal with a full-screen view, matching the workflow execution UX and providing more screen real estate to diagram

Fixes #1027

Changes

• New shared header component
• Replace diagram editor modal with full screen view

Testing

Test Plan

• Unit tests added/updated
• Integration tests added/updated (if applicable)
• Tested manually (describe below if applicable)

Manual Testing

Manually checked all example workflows

Checklist

Before submitting this PR, please ensure:

• I ran the full build with integration tests locally: ./mvnw clean install -DskipITs=false
  • Ran make quick-check
• Code follows the project's code conventions
• Tests have been added/updated to cover the changes
• Documentation has been updated (if user-facing changes)
• Commit messages are clear and follow conventional commits style
• I have read and followed the Contributing Guide
• I have read and comply with the LLM Usage Policy (if applicable)

Additional Notes

Before

Screen.Recording.2026-09-30.at.13.23.00.mov

After

Screen.Recording.2026-09-30.at.13.26.48.mov

[mathecruz]

It is really looks better now! Thanks!