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

internal/starlink/pb/starlink.proto

@@ -0,0 +1,74 @@
+// A minimal slice of the Starlink dish's local gRPC API: just the one
+// unary RPC (SpaceX.API.Device.Device/Handle) and the get_status request
+// and dish status response, reduced to the handful of fields rtnetmon
+// shows. The proto package name and field numbers must match the dish
+// exactly for the wire format to line up; every other field the dish sends
+// is ignored as an unknown field.
+//
+// Field numbers, message names and the DishState enum are transcribed from
+// the community-maintained pre-generated bindings at
+// github.com/starlink-community/starlink-grpc-go, commit
+// 2e89f3d7e3092adecbcc04e9e003e61ed5f7c6a3 (get_status = 1004,
+// dish_get_status = 2004). They are not verified against a live dish here.
+//
+// Regenerate with:
+//   protoc --go_out=. --go_opt=paths=source_relative \
+//          --go-grpc_out=. --go-grpc_opt=paths=source_relative \
+//          internal/starlink/pb/starlink.proto
+
+syntax = "proto3";
+
+package SpaceX.API.Device;
+
+option go_package = "git.eeqj.de/sneak/rtnetmon/internal/starlink/pb;starlinkpb";
+
+service Device {
+  rpc Handle(Request) returns (Response);
+}
+
+message Request {
+  oneof request {
+    GetStatusRequest get_status = 1004;
+  }
+}
+
+message GetStatusRequest {}
+
+message Response {
+  oneof response {
+    DishGetStatusResponse dish_get_status = 2004;
+  }
+}
+
+message DishGetStatusResponse {
+  DeviceState device_state = 2;
+  DishObstructionStats obstruction_stats = 1004;
+  DishAlerts alerts = 1005;
+  DishState state = 1006;
+  float pop_ping_drop_rate = 1003;
+  float downlink_throughput_bps = 1007;
+  float uplink_throughput_bps = 1008;
+  float pop_ping_latency_ms = 1009;
+}
+
+message DeviceState {
+  uint64 uptime_s = 1;
+}
+
+message DishObstructionStats {
+  float fraction_obstructed = 1;
+}
+
+message DishAlerts {
+  bool motors_stuck = 1;
+  bool thermal_shutdown = 2;
+  bool thermal_throttle = 3;
+  bool unexpected_location = 4;
+}
+
+enum DishState {
+  UNKNOWN = 0;
+  CONNECTED = 1;
+  SEARCHING = 2;
+  BOOTING = 3;
+}