Multiple people: an admin adds users and chooses which tabs each may use

- Accounts: the setup code (or an existing single-user install, migrated automatically) creates the admin;
  the admin adds people in Settings -> People and gives each a one-time invite code to enrol their own passkey
- Each person's tasks, NE Hub events and subscribe link, settings, calendar links, iCloud connection and Plex
  sign-in are private, stored in their own folder (/data/users/<id>/); Plex sign-in moved from browser cookies
  into that folder (encrypted), so it also follows them across devices
- Tab access is enforced by the server (403) and reflected in the app (nav, Home, Settings, search, /api/config
  hides addresses of tabs a person cannot use); browser storage is namespaced per person
- Admin tools: change tabs, invite a device, sign out everywhere (session epoch), turn off, make/remove admin,
  delete a person and their data; the last admin cannot be removed
- Sessions carry the person (uid.epoch.expiry.signature); old single-user cookies still work as the admin
- tools/users-test.js (83 checks: isolation, access limits, invites, sign-out/disable/delete, Plex and iCloud
  per person, migration) now runs in the Gitea workflow before the image is built

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

vault.js

@@ -0,0 +1,12 @@
+// Small helper to keep a secret value encrypted at rest (AES-256-GCM, key derived from the server secret).
+const crypto = require('crypto');
+const auth = require('./auth');
+module.exports = label => {
+  let key; const k = () => key || (key = crypto.scryptSync(auth.secret, label, 32));
+  return {
+    seal(obj) { const iv = crypto.randomBytes(12), c = crypto.createCipheriv('aes-256-gcm', k(), iv);
+      const d = Buffer.concat([c.update(JSON.stringify(obj), 'utf8'), c.final()]); return Buffer.concat([iv, c.getAuthTag(), d]).toString('base64'); },
+    unseal(s) { try { const b = Buffer.from(s, 'base64'), d = crypto.createDecipheriv('aes-256-gcm', k(), b.subarray(0, 12));
+      d.setAuthTag(b.subarray(12, 28)); return JSON.parse(Buffer.concat([d.update(b.subarray(28)), d.final()]).toString('utf8')); } catch { return null; } },
+  };
+};