Add Theme menu to apply custom themes via javascript/UI/themes.js (with persistence)

[rabail-aamir]

Description

The PR adds a Theme menu to the header which connects to existing theming utilities to enable users to apply SKO custom themes through the console without needing it.

Type of change

UI: Unhide the theme selector in index.html.
Behavior: Populate the dropdown from themes (in javascript/UI/themes.js), apply the chosen theme via applyTheme(theme), and include a “Default / None” option to reset to base styles.
Persistence: Save/restore the last selected theme in localStorage (skoTheme).

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• [ ✔] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as
  expected)
• Documentation (update or new)

How Has This Been Tested?

• Run SKO locally and load the app.
• In the header, open Theme and select each option (e.g., light, dark, professional-grey, space).
• Observe colors update immediately (CSS variables change).
• Refresh the page — the selection should persist.
• Choose Default / None — styles reset to base.

Testing Checklist

• [✔ ] Tested in latest Chrome
• [✔ ] Tested in latest Safari
• [✔ ] Tested in latest Firefox

Checklist

• [✔ ] My code follows the style guidelines of this project
• [✔] I have performed a self-review of my own code
• [✔ ] I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• [✔ ] My changes generate no new warnings
• I have requested a review from ... on the Pull Request

[rabail-aamir]

[Oliver-Quail]

Hi @rabail-aamir,
This looks like a good PR.
Please can you revert the changes to package-lock.json and package.json then I'll be happy to approve this PR.
Also if you could add documentation as to how to add a theme as your next PR that would be amazing! :)

[Oliver-Quail]

I approve this PR

[liammcknightt]

I approve this PR and have moved it to Mentor Review.

[github-actions]

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