Add Starlink status lines for the physical gateway pane (closes #3)

When the non-VPN physical gateway is a Starlink dish, two lines are shown
under that pane: state, uptime, obstruction and alert count; then pop-ping
latency and drop rate with downlink/uplink throughput. They turn red when
the dish is not connected or an alert is active.

Detection is a TCP connect to the dish's fixed endpoint 192.168.100.1:9200,
bound to the physical interface the same way the latency probes bind. Until
a dish answers nothing is drawn and no status is fetched, so an absent dish
adds no noise. Status comes from the dish's local get_status gRPC call.

Detection and the fetch sit behind a small Client interface; the loop and
the pure Render function are tested with a fake, no dish and no network.

Model: opus-4-8

README.md

@@ -67,6 +67,21 @@ Anything outside this matrix — on Linux, only one of the named pair present, o
 no/multiple default routes when neither is present; on macOS, no default route
 or more than one physical default route — exits with a clear error.
 
+## Starlink status
+
+When the non-VPN physical gateway is a Starlink dish, two extra lines appear
+under that pane: dish state, uptime, obstruction and alert count on the first,
+and pop-ping latency and drop rate with downlink/uplink throughput on the
+second. They turn red when the dish is not connected or an alert is active.
+
+Detection is a TCP connect to the dish's fixed local endpoint,
+`192.168.100.1:9200`, made over the physical interface (the same binding the
+latency probes use). The dish sits behind the Starlink router, so this is not a
+gateway-address check. rtnetmon probes once a minute until a dish answers and
+then reads its status every few seconds; when no dish answers, nothing is drawn
+and no status is fetched. The status comes from the dish's local `get_status`
+gRPC call.
+
 ## Installation
 
 ```bash
@@ -107,6 +122,10 @@ rtnetmon/
 │   │   ├── netdetect.go     # selection logic and route parsers (pure)
 │   │   ├── routes_linux.go  # Linux default-route query (build-tagged)
 │   │   └── routes_darwin.go # macOS default-route query (build-tagged)
+│   ├── starlink/       # Starlink dish detection and status
+│   │   ├── starlink.go      # Status, Client interface, pure Render
+│   │   ├── client.go        # real gRPC client (get_status)
+│   │   └── pb/              # generated bindings for the get_status RPC
 │   └── monitor/        # core monitoring functionality
 │       ├── monitor.go       # monitor types, probes, logging
 │       ├── loops.go         # monitoring loops (reachability, loss, TCP)