[Feature] Family features: server-backed PIN, QR approval, managed accounts, time limits #541

What problem does this solve?

The same gaps as the Moonfin-Core proposal (Moonfin-Client/Moonfin-Core#1912). In Smart-TV specifically:

• The sign-in PIN (pinCodeProtection, pinCodeHash) lives in local settings only and isn't
  in SYNCABLE_KEYS, so it differs per TV.
• Nothing nudges an admin to set a PIN.
• The Quick Connect login shows a code only.
• Access schedules aren't handled: a denied login isn't distinguished from other 403s, and
  there is no time-limit experience.

Proposed solution

Parity with Moonfin-Core, in this order, each as its own PR:

1. QR on Quick Connect. utils/qrCanvas.js already draws QR codes for other dialogs.
2. Time's up. Handle schedule denials at login and enforce the window in the app,
   including during playback. No plugin needed. Re-evaluate on resume, since webOS can
   suspend the app.
3. Server-backed PIN (needs the plugin proposal) reusing pinLockout.js, with the
   local PIN as fallback. An admin PIN prompt after sign-in only when no server-side
   PIN is available (plugin absent or unusable).
4. Managed accounts (needs the plugin proposal): filter the picker to the users the signed-in
   admin manages, plus a "Set up Family Accounts" action in that admin's settings. The app
   already has the Quick Connect initiate and exchange calls and keeps several users'
   tokens, so this adds one /QuickConnect/Authorize request.

Everything must work without the plugin.

Platform

webOS, Tizen

Server

Jellyfin

Alternatives considered

Waiting for Core to land first and following its implementation. Fine by me if you prefer that order.

Additional context

• Plugin proposal: [Feature] Managed accounts and server-side PIN Plugin#328. Core proposal: [Feature] Family features: admin PIN, QR approval, managed accounts, time limits Moonfin-Core#1912.
• I used an AI assistant (Claude) to help research and draft this and will disclose it on
  each PR. I can test on webOS. I have no Tizen device, so Tizen changes will be untested by me and I'd appreciate a maintainer or contributor checking them.