fix: WireGuard routing, DNS, service access, and UI improvements

- Fix CoreDNS not loading .cell zones (wrong Corefile path, now uses -conf flag)
- Fix WireGuard server address conflict (172.20.0.1/16 overlapped with Docker
  network; changed to 10.0.0.1/24 to eliminate duplicate routes)
- Add SERVERMODE=true and sysctls to WireGuard docker-compose for server mode
- Fix DNS zone file parser to handle 4-field records (name IN type value)
- Add get_dns_records() to NetworkManager; mount data/dns into API container
- Fix peer config endpoint: look up IP/key from registry, use real endpoint
- Add bulk peer statuses endpoint keyed by public_key
- Normalize snake_case API fields to camelCase in WireGuard UI
- Add port check endpoint (checks via live handshake, not unreliable TCP probe)
- Add Caddy virtual hosts for ui/calendar/files/mail .cell domains (HTTP only)
- Fix cell config domain default from cell.local to cell
- Fix Routing Network Config tab (was calling hardcoded localhost:3000)
- Fix DNS records display (record.value not record.ip)
- Move service access guide to top of Dashboard with login hints
- Add /api/routing/setup endpoint

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

config/mail/mailserver.env

@@ -0,0 +1,3 @@
+OVERRIDE_HOSTNAME=mail.cell.local
+POSTMASTER_ADDRESS=admin@cell.local
+LOG_LEVEL=warn