Fix: Download pdf button, Standardize pdf Handling and Deployment with _static/

Hey @lorfrolinux, this PR updates pdf handling to ensure consistency between local builds and GitLab Pages deployment, using _static/ as the standard location fixes pdf download button:

Deployment Script:

• Changed PDF move from public/proposals/ to public/_static/.
• Added rm -rf public/html to clean up after moving HTML to public/, alongside doctrees and latex.
• Swapped build order (PDFs before HTML) for consistency.

Pdf Button Template:

• Updated href from {{proposal_name}}.pdf to {{ pathto('_static/' ~ proposal_name.split('/')[-1] ~ '.pdf', 1) }}.
• Simplified pagename == proposal_name check for nested proposal paths.

conf.py:

• Added copy_pdfs function to copy PDFs from _build/latex/ to _build/html/_static/ on build-finished.
• Ensures local builds match deployment’s _static/ structure.

This aligns with Sphinx’s _static/ convention, fixes path mismatches, and tested it, successfully works locally and when deployed. Please review and let me know if anything changes required.