fix(website): prioritize desktop downloads and clarify app identity

[devswha]

Summary

• Keep the product positioned as the desktop app for Gajae Code, with matching page and social metadata.
• Put visible macOS and Linux download actions ahead of source/server options, and bring the existing real-session screenshot directly below the hero.
• Add the published Linux x64 DEB and AppImage artifacts and their individual checksums; separate desktop installers from the self-hosted web/server options.
• Preserve the existing visual style, release pin, screenshots, dependencies, and GitHub Pages deployment.

Validation

• npm test --prefix website: 14 tests passed, covering release filenames, checksum/version consistency, positioning, section order, accessibility references, and download separation.
• npm run build --prefix website: passed.
• npm run verify: passed (existing environment-gated skips unchanged).
• All four published beta.9 artifacts responded HTTP 200; all four SHA-256 sidecars responded HTTP 200 and named the corresponding artifact.
• Browser review at desktop, tablet, and narrow/mobile viewport sizes: no document horizontal overflow; first screenshot visible within the initial desktop/mobile view; Linux and server anchors navigate to the correct sections; Linux target receives focus; no browser console errors.

Only six website files change. App, release, and other concurrent work are untouched. No dependency or hosting migration is included.