Bump theme to 0.4.7

[svekars]

• Bump pytorch_sphinx_theme2 version from 0.4.6 to 0.4.7
• Update CHANGELOG with changes since v0.4.6:
  • Markdown generation for LLM docs (PR Add HTML-to-markdown generation for llms.txt #239)
  • Collapsible list component for C++ docs (PR Add collapsible styles for C++ docs #240)
  • Right nav scroll fix (PR Add collapsible styles for C++ docs #240)
  • Google search thumbnail fix (PR Fix red X thumbnail appearing in Google search results #241)
• Published to PyPI: https://pypi.org/project/pytorch-sphinx-theme2/0.4.7/

Test plan

• Verify package installs correctly: pip install pytorch_sphinx_theme2==0.4.7
• Verify docs build with the new version

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