User invites & KV infrastructure

Features User invitations Admins can create invite links Can be single or multi use Can have a custom expiry date Invite management added to a new admin "Invites" tab Admins can receive optional email notifications when new users sign up Email verification Email verification now required on sign up Improvements made to email verification flow on email change Admin page restructure Admin page reorganized and split into tabbed sections: Settings, Stats, Users, Invites Can be navigated with number keys like with the Manage pages in app Infrastructure Redis / KV store Added Redis (or Upstash) as a key-value store for OTP codes and rate limiting If not present, will fall back to in-memory storage Fixes and improvements Header and footer auto-hide on scroll down in article view (and show on scroll up) Fixed mobile drawer sliding off-screen when keyboard is visible Fixed tag pagination in add/edit dialogs Fixed an issue where new feed items wouldn't show up without a full reload Updated Docker image references for repo move to megaflorasoftware/serial