Add Starlink status lines for the physical gateway pane (closes #3) (#7)

Detection is a TCP connect to the dish endpoint bound to the physical
interface; once a dish answers, get_status is read every 5s and two
status lines render under the physical pane, red on disconnect or
alert. No dish: nothing drawn, no RPC. Minimal vendored proto bindings
for get_status only. Independent review passed (PR 7 comment 100012).

Model: opus-4-8 (implementation and review); model: claude-fable-5
(merge)

internal/starlink/starlink.go

@@ -0,0 +1,81 @@
+// Package starlink detects a Starlink dish on the local network and reads a
+// short status summary from the dish's local gRPC endpoint. Detection and
+// the status fetch sit behind the Client interface, so the monitor is
+// tested with a fake and needs no dish and no network. Render turns a
+// Status into the two lines the UI draws and is a pure function.
+package starlink
+
+import (
+	"context"
+	"fmt"
+	"time"
+)
+
+// Address is the dish's fixed local gRPC endpoint. Every dish answers here
+// from behind the Starlink router, whatever the LAN's own addressing is, so
+// this is not the default gateway (that is the router).
+const Address = "192.168.100.1:9200"
+
+// StateConnected is the dish state string that means the link is up; any
+// other state is treated as an alert condition by Render.
+const StateConnected = "CONNECTED"
+
+// Units used when reducing the dish's raw values to display values.
+const (
+	percentScale   = 100.0
+	bitsPerMegabit = 1_000_000.0
+	hoursPerDay    = 24
+	minutesPerHour = 60
+)
+
+// Status is the subset of the dish's get_status response that rtnetmon
+// shows. Throughput is megabits per second; obstruction and drop are
+// percentages on a 0..100 scale.
+type Status struct {
+	State          string
+	Uptime         time.Duration
+	ObstructionPct float64
+	Alerts         int
+	PopPingMs      float64
+	PopPingDropPct float64
+	DownlinkMbps   float64
+	UplinkMbps     float64
+}
+
+// Client probes for a dish and reads its status. The real implementation
+// speaks gRPC to Address over one bound interface; tests use a fake.
+type Client interface {
+	// Probe reports whether a dish answers on Address over the bound
+	// interface. It is cheap: a TCP connect, no gRPC call.
+	Probe(ctx context.Context) bool
+	// Status fetches the dish's current status.
+	Status(ctx context.Context) (Status, error)
+}
+
+// Render formats a Status as the two status lines drawn under the physical
+// pane, and reports whether they warrant an alert (red) color: the dish is
+// not connected, or an alert is active.
+func Render(s Status) (string, string, bool) {
+	line1 := fmt.Sprintf(
+		"Starlink: %s  uptime %s  obstruction %.1f%%  alerts %d",
+		s.State, formatUptime(s.Uptime), s.ObstructionPct, s.Alerts)
+	line2 := fmt.Sprintf(
+		"  pop ping %.0fms / drop %.1f%%  down %.1fMbps / up %.1fMbps",
+		s.PopPingMs, s.PopPingDropPct, s.DownlinkMbps, s.UplinkMbps)
+	alert := s.State != StateConnected || s.Alerts > 0
+
+	return line1, line2, alert
+}
+
+// formatUptime renders a duration as whole days, hours and minutes.
+func formatUptime(d time.Duration) string {
+	if d < 0 {
+		d = 0
+	}
+
+	days := int64(d / (hoursPerDay * time.Hour))
+	hours := int64(d/time.Hour) % hoursPerDay
+	mins := int64(d/time.Minute) % minutesPerHour
+
+	return fmt.Sprintf("%dd %dh %dm", days, hours, mins)
+}