feat(headscale): print OIDC callback URL after deploy

Surface https://${HEADSCALE_DOMAIN}/oidc/callback in the final DEPLOYED
summary so it's easy to register in the pocket-id OIDC client.

deployments/headscale/deploy.sh

@@ -287,6 +287,9 @@ Tailnet:     ${TAILNET_DOMAIN} (MagicDNS suffix)
 OIDC:        https://${POCKETID_DOMAIN}
 Stack dir:   ${STACK_DIR}
 
+OIDC redirect/callback URI -- register THIS in your pocket-id client:
+  https://${HEADSCALE_DOMAIN}/oidc/callback
+
 Bootstrap a user (run from $STACK_DIR):
   docker compose exec headscale headscale users create alice
   docker compose exec headscale headscale users list