website: redirect /manualpages to release/manualpages
website: add redirect from https://petsc.org/community/meetings/2025 to https://petsc.org/release/community/meetings/2025
website: fix 'docs' redirect for all manpages
website: add in a redirect for old URLs with 'release/docs'
website: download URL changed - so add a redirect for the old one
Docs: 404.html: fix typo
website: add 404 instructions. Also copy website files from docs/public