GSOC-E2E: Add unauth-to-auth sketch persistence test.

[Geethegreat]

Issue:

Fixes #

Added a Playwright E2E test covering the unauthenticated-to-authenticated user workflow.

Demo:

e2e-ath-unath-flow.mp4

Changes:

• Verifies that a guest user can write and execute a sketch before creating an account.
• Confirms that attempting to save as an unauthenticated user prompts account creation.
• Completes the signup flow through the UI.
• Verifies that the authenticated session is established successfully after signup.
• Ensures the sketch persists and can be executed successfully after the user becomes authenticated.
• Opens the verification link in the mail and confirms redirection to the editor.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines

[clairep94]

take this out as it's covered in the first test on this page