A vX.Y.Z tag used to ship both JARs under the Paper version number, so the
Velocity version never appeared in a tag. Changelog download links guessed
paper/ and velocity/ tags that did not exist and returned 404, and the same
JAR resurfaced under several releases.

Paper now releases on vX.Y.Z and Velocity on velocity/vX.Y.Z, which matches
the CHANGELOG.md headings one to one. Paper keeps the bare form rather than
moving to paper/vX.Y.Z because the update checker in already-deployed Paper
builds only understands that form. Both workflows call a shared reusable
workflow, since the two had drifted into near-identical copies.

Co-Authored-By: Claude <noreply@anthropic.com>

Release notes were written into the GitHub release body, which means they exist
once, in English only, and are awkward to revise after publishing. Putting them
on the site gives each release a Japanese and an English page that can be
corrected later and linked from anywhere.

The overview page states the versioning rules the version numbers alone do not
convey: that dropping a supported platform is a MINOR bump, that the Paper and
Velocity builds advance separately, and that the plugin version says nothing
about compatibility.

Co-Authored-By: Claude <noreply@anthropic.com>

- Add download page with GitHub API data loader for latest releases
- Add DownloadCard Vue component with JA/EN i18n support
- Include Modrinth and CI build links
- Rename docs/ directory to website/

Co-Authored-By: Claude <noreply@anthropic.com>