Point TaskTape to the verified public beta

[codeswithroh]

What changed

• point README downloads to the verified Vercel production site
• remove GitHub Pages deployment because the account-level custom domain redirected to an unresolvable host
• record the complete CDN download, checksum, disk-image, desktop, and mobile checks
• mark the public beta milestone complete with the notarization boundary still explicit

Verified

• https://tasktape-replay.vercel.app/ returned 200 on desktop and mobile, with loaded images, no overflow, and no console errors
• the stable GitHub URL downloaded all 300,282,253 bytes
• downloaded SHA-256 matched a63e6d0791a7fc97d93be02ec8e52fbb6bcf276f5ef8324d799550e4fbaf4c89
• downloaded DMG passed hdiutil verify