fix: widen Settings modal to two columns; env cleanup

- SettingsModal: widen to sm:max-w-3xl with max-h-[90vh] scroll and a
  two-column grid so it no longer overflows the viewport. Left column =
  status/service checks + canvas prefs; right column groups all auto-sync
  config (Zigbee, Z-Wave, Proxmox).
- .env.example: drop ZIGBEE_/ZWAVE_ SYNC_ENABLED + SYNC_INTERVAL — the
  auto-sync activation is configured in the Settings modal (persisted to
  scan_config.json), same as Proxmox; connection config stays env-only.

ha-relevant: no

.env.example

@@ -71,8 +71,6 @@ MCP_SERVICE_KEY=svc_changeme
 # ZIGBEE_BASE_TOPIC=zigbee2mqtt
 # ZIGBEE_MQTT_TLS=false                # true for TLS brokers (typically port 8883)
 # ZIGBEE_MQTT_TLS_INSECURE=false       # skip cert verify (self-signed only; requires TLS)
-# ZIGBEE_SYNC_ENABLED=false            # turn scheduled auto-sync on
-# ZIGBEE_SYNC_INTERVAL=3600            # seconds between syncs (min 300)
 
 # Z-Wave JS UI (zwavejs2mqtt) auto-sync — same MQTT secret/env rules as Zigbee.
 # ZWAVE_MQTT_HOST=192.168.1.20
@@ -83,5 +81,3 @@ MCP_SERVICE_KEY=svc_changeme
 # ZWAVE_GATEWAY_NAME=zwavejs2mqtt
 # ZWAVE_MQTT_TLS=false                 # true for TLS brokers (typically port 8883)
 # ZWAVE_MQTT_TLS_INSECURE=false        # skip cert verify (self-signed only; requires TLS)
-# ZWAVE_SYNC_ENABLED=false             # turn scheduled auto-sync on
-# ZWAVE_SYNC_INTERVAL=3600             # seconds between syncs (min 300)