Fix issue #431 : Confusing UI/UX for Theme Switcher Button

[Risika-25]

Description of Changes

This Pull Request improves the theme switcher UX by displaying the theme that will be applied after clicking instead of the currently active theme. This will make the toggle behavior clearer and more intuitive for users.

Related Issue

Fixes #431

Type of Change

Please check the appropriate box that describes your PR:

• 🐛 Bug Fix — Fixes a documented issue or incorrect behavior
• [ x ] ✨ Content Enhancement — Updates or improves existing content
• ✍️ New Content — Adds new chapters, examples, or significant sections
• 🛠️ Other — Please describe in the Description of Changes section

Additional Notes (Optional)

Checklist

• I have searched open pull requests to avoid duplicates.
• I have built the book locally using the build instructions and verified my changes work as expected.
• I have written clear, conventional commit messages, as per the Pull Request Guidelines.

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