Playwright: Verifying theme configuration workflows through automation under Preferences.

[ved-bruno]

Description

This PR adds automated tests using Playwright to verify the correct functionality of application theme selection workflows under the Preferences section.

Jira link to track this task: https://usebruno.atlassian.net/browse/BRU-1028

Contribution Checklist:

• [ ] The pull request only addresses one issue or adds one feature.
• [ ] The pull request does not introduce any breaking changes
• [ ] I have added screenshots or gifs to help explain the change if applicable.
• [ ] I have read the contribution guidelines.
• [ ] Create an issue and link to the pull request.

Note: Keeping the PR small and focused helps make it easier to review and merge. If you have multiple changes you want to make, please consider submitting them as separate pull requests.

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