DOC: Simplify pandas theme footer
# 🎯 DOC: Simplify pandas theme footer

## 📝 Description
This pull request refactors the pandas documentation footer by tapping into the built-in templates in **pydata-sphinx-theme** v0.16. The result is a leaner, more maintainable setup with zero visual regressions—science approved!

## 🔧 Changes Made
1. **`doc/source/conf.py`**
   - Updated the copyright line to include “pandas”  
   - Swapped out custom footer bits for the theme’s built-in templates:
     ```python
     html_theme_options = {
         "footer_start": [
             "copyright",
             "pandas_footer",
             "sphinx-version",
         ],
         …
     }
     ```
2. **`doc/_templates/pandas_footer.html`**
   - Removed the now-redundant copyright snippet  
   - Kept only the NumFOCUS & OVHcloud sponsor links  
3. **`doc/source/_static/css/pandas.css`**
   - Added horizontal layout rules for the new footer items  
   - Ensured consistent spacing & alignment  
4. **`doc/source/whatsnew/v3.0.0.rst`**
   - Added a “Documentation changes” section  
   - Linked to issue [#51536](https://github.com/pandas-dev/pandas/issues/51536)

## ✅ Benefits
- **DRY**: Eliminates duplicated footer code  
- **Maintainable**: Leverages standard theme hooks  
- **Consistent**: Visual appearance remains identical  
- **Future-proof**: Automatically picks up theme updates  

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🚀 All checks have passed and this PR is ready for merge! 🎉

this is AI generated? Thanks for the PR, but we discourage the use of AI generated pull requests so closing