feat(setup): Cluster-Node-Modus im Setup-Wizard + Install-Script-Port-Fix

Setup-Wizard zeigt jetzt beim ersten Aufruf eine Modusauswahl:
- "Neuinstallation" → bisheriger Flow (Admin-Account + FQDN + ACME)
- "Cluster-Knoten beitreten" → nur FQDN + ACME, kein Admin-Account;
  nach dem Submit werden die cluster-join-Befehle direkt angezeigt

Backend: NodeRequest + Store.CompleteAsNode() + POST /setup/complete-node
State: is_cluster_node Flag; login via PG-Replikation vom Primary

Install-Script: Setup-URL zeigt jetzt korrekt :3443/setup statt /setup

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/install.sh

@@ -183,9 +183,10 @@ echo -e "  ${DIM}━━━━━━━━━━━━━━━━━━━━━
 echo ""
 echo -e "  ${GRN}${BLD}Installation complete!${NC}"
 echo ""
-print_url "Setup wizard" "/setup"
+print_url "Setup wizard" ":3443/setup"
 echo ""
 echo -e "  ${DIM}Open the URL in your browser to configure EdgeGuard.${NC}"
+echo -e "  ${DIM}(Port 3443 is the management UI — separate from the public :443 frontend.)${NC}"
 echo -e "  ${DIM}(SSL is self-signed on first boot — confirm the browser warning;${NC}"
 echo -e "  ${DIM} a real Let's Encrypt cert is issued after the FQDN is set.)${NC}"
 echo ""