v0.5.1: shareable no-login remote-control links

Added

• Shareable no-login "remote control" links: the host can mint a link (/r/<token>) that exposes just
  one guest's speed-dial pad (its 0-9 buttons) as a responsive page, hand it to someone with no Telegram
  account or login, and revoke it any time. Fail-closed by design: minting and use both require web login
  (auth mode simple), only the predefined pad slots fire, requests are per-token rate limited and
  noindex/no-store, and the share token authenticates nothing on the API. Manage them in Settings, Access:
  1 / 7 / 30-day expiry, an optional label, and an active-link list with revoke.