[AlxcBTW]

Adds /download, the next step of the redesign a player meets after the home page.

• One button for the visitor's own system (Windows installer, Mac zip or Linux AppImage), size and version from the latest GitHub release; phones are told the launcher is for computers.
• A ledger of every release file (Windows installer and one-file exe, macOS Apple silicon, Linux AppImage, Flatpak, tar.gz), SHA256SUMS and release notes.
• What 0.3.5 brings: the six looks painted from the launcher's own shader tones, Played With Recently, language list, reduced motion.
• Fallback when GitHub does not answer: links to the latest release and a status note instead of missing numbers.
• The download menu lists macOS as a real download (0.3.5 ships it); nav and footer point to /download; footer and pill styles extracted so both pages share them.
• Tests: release parsing, file rows, e2e with axe at desktop and phone.

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