[KeyffMS]

Addresses #99.

Implements the static SightAdapt™ product site from the completed #124 content contract:

• dependency-free responsive HTML/CSS under site/;
• Home, Features, Download, Documentation, How it works, FAQ, Releases, Privacy, Legal, Security and Support;
• canonical SightAdapt brand assets copied from the repository;
• current immutable v0.5.0.50-alpha release metadata, direct binary link and SHA-256 verification;
• semantic structure, skip navigation, keyboard-visible focus, meaningful image alternatives and a text-accessible architecture diagram;
• no cookies, analytics, remote fonts, tracking scripts or unsolicited third-party embeds;
• relative paths compatible with both the GitHub Pages /SightAdapt/ fallback and production /sightadapt/;
• tools/test-site.ps1 validation added to the main CI;
• GitHub Pages deployment only after a successful main build.

Repository-admin work remains external to this PR: #87 still requires actual main protection, and GitHub Pages must be enabled with GitHub Actions as its source before first deployment can succeed.