feat: escape to exit preview mode

[shreyanshkotak]

Description

1. Related to Annoying things #5501. This lets user escape exit preview mode when triggered from the builder UI, while preserving canvas-originated escape behavior so preview mode remains active when the canvas should handle the key event.

Steps for reproduction

1. Open the builder and switch to preview mode.
2. Press Escape from the builder UI.
3. Expect preview mode to exit and the sidebar panel to return to auto.
4. Switch to preview mode again.
5. Press Escape while the focused inside the canvas.
6. Expect preview mode to stay active and canvas/native page behavior to be preserved.

Code Review

• hi @kof, I need you to do
  • conceptual review (architecture, feature-correctness)
  • detailed review (read every line)
  • test it on preview

Before requesting a review

• made a self-review
• added inline comments where things may be not obvious (the "why", not "what")

Before merging

• tested locally and on preview environment (preview dev login: 0000)
• updated test cases document
• added tests
• if any new env variables are added, added them to .env file

[github-actions]

🚀 Deployed!

📍 Preview: https://pr-5730.development.webstudio.is

Note: Adding new commits will remove the safe-to-deploy label and require re-approval.

[kof]

Merged, thank you!