Fix: NumFOCUS footer logo missing on Tag pages

[Aman-G-upta]

Description of Changes

This pull request fixes a missing NumFOCUS logo in the footer across all tag-generated pages (_tags/*.html).
While the main pages display the correct NumFOCUS footer, the tag pages were missing the logo due to the footer script not being applied consistently to generated tag templates.

I updated the footer logic so that the NumFOCUS images correctly appear across all tag pages in both light and dark mode.
This improves consistency and branding across the site.

Related Issue

Closes #432

Type of Change

Please check the appropriate box that describes your PR:

• 🐛 Bug Fix — Fixes a documented issue or incorrect behavior

Additional Notes (Optional)

Verified locally that the footer now correctly displays:

NumFOCUS logo in light mode
NumFOCUS logo in dark mode

After fix

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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