contacts: Contrack as the robust contacts (C3), picked in Settings or the setup wizard

Spec 11 §4: contacts.provider and contacts.contrack (local address only, company token
write-only), each person's own token (users.contrack_token_enc, migration 0010) in My settings,
books read from Contrack with a 5-minute cache, Add to contacts and accepted shares created in
Contrack, the company account on desk phones. Setup wizard step 8 Contacts. deploy/contrack
(2.0.2, pinned), Caddy/nginx blocks, decision 0003, admin guide Contacts. Tested against a fake
and a real Contrack 2.0.2 (contrack-live.test.ts).

docker-compose.yml

@@ -87,6 +87,7 @@ services:
     network_mode: host
     environment:
       PUBLIC_HOSTNAME: ${PUBLIC_HOSTNAME:?set in .env}
+      CONTRACK_HOSTNAME: ${CONTRACK_HOSTNAME:-} # deploy/caddy/Caddyfile, when Contrack runs
     volumes:
       - ./deploy/caddy/Caddyfile:/etc/caddy/Caddyfile:ro
       - ./data/caddy:/data