Add full Docker deployment: setup.sh, update.sh, healthcheck, TURN support

- setup.sh: interactive/non-interactive one-shot installer (build, DB
  healthcheck, migrate, seed, start), idempotent secret generation, NPM
  reverse-proxy network auto-detection and optional join, optional
  AUTO_UPDATE cron install.
- update.sh: release-tag-gated updates only (never bare main), DB backup
  with retention before every update, lock file against concurrent runs,
  automatic code rollback on failed post-update healthcheck.
- Dockerfile: multi-stage build, non-root user, built-in HEALTHCHECK against
  the new /api/health route, wholesale COPY so new source dirs (e.g.
  scripts/) never silently go missing at runtime.
- docker-compose.yml: internal anouma-network (configurable), named volume
  for Postgres, app depends_on postgres healthy, no unnecessary published
  ports; docker-compose.override.yml.example documents joining an existing
  NPM network without ever touching NPM itself.
- Fix host-detection: isHost was Boolean(user), wrongly granting host
  privileges to logged-in customers; now checks user.collection === "users".
- Wire configurable STUN/TURN servers through to the WebRTC client
  (lib/meeting/iceServers.ts) so a TURN server can be added later via env
  vars only, no code changes.
- DEPLOYMENT.md, updated README.md and .env.example documenting the whole
  flow: NPM integration, env vars, WebRTC, updates, backups, rollback.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/(frontend)/termine/[slug]/page.tsx

@@ -39,7 +39,9 @@ export default async function EventDetailPage({ params }: Args) {
   if (event.isOnline) {
     const payload = await getPayload({ config });
     const { user } = await payload.auth({ headers: await headers() });
-    const isHost = Boolean(user);
+    // Must check the collection, not just presence — a logged-in customer
+    // (collection "customers") must never be treated as host.
+    const isHost = user?.collection === "users";
     const settings = await payload.findGlobal({ slug: "meeting-settings" });
     const start = combineDateAndTime(event.date, event.startTime);
     const end = event.endTime