router-status: replace Cockpit's Van Router plugin with MQTT -> Home Assistant

Cockpit's login was unreliable (Firefox rejected sometimes, Android failed
outright with a TLS handshake error) and it was a resource hog on this Pi.
van-router-mqtt publishes the same AP/client/WAN/Starlink/modem status and
accepts the same control actions (AP/modem restart, WAN connect/disconnect,
prefer) via MQTT with HA discovery, using the local Mosquitto broker already
running here. It republishes van-failover/van-thermal's own state.json files
verbatim rather than modifying either daemon (van-thermal is deliberately
stdlib-only; van-failover's control loop wasn't worth an added dependency).

Adds a Lovelace dashboard (ha/dashboards/van-router.yaml) consuming those
entities. Cockpit's plugin is left deployed for now, not yet retired.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S2tpeaiHUriQbbnQ4SCbkf

router-status/config.json

@@ -0,0 +1,17 @@
+{
+  "broker": "localhost",
+  "port": 1883,
+  "client_id": "van-router-mqtt",
+  "device_id": "van_router",
+  "discovery_prefix": "homeassistant",
+  "state_root": "van/router",
+  "cmd_root": "vanlink/cmd",
+  "poll_interval_s": 5,
+  "wifi_5g_iface": "@WIFI_5G_IFACE@",
+  "wifi_2g_iface": "@WIFI_2G_IFACE@",
+  "lan_usb_iface": "@LAN_USB_IFACE@",
+  "starlink_iface": "@STARLINK_IFACE@",
+  "starlink_dish": "192.168.100.1:9200",
+  "modem_usb_vendor": "@MODEM_USB_VENDOR@",
+  "wifi_wan_iface": "wlan0"
+}