Add CACHE_STATUS UART poll and dashboard live stream.

Combine cached accel and tap in one low-overhead master command for ~16 ms
host polling. The dashboard uses a single live-stream toggle plus per-slave
accel-stream controls; fix live_stream state so polling is not cleared every
slow client refresh.

Co-authored-by: Cursor <cursoragent@cursor.com>

goTool/cmd_cache_status.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+)
+
+func runCacheStatus(sp *serialPort) error {
+	r, err := sp.readCacheStatus()
+	if err != nil {
+		return err
+	}
+	accel := r.GetAccel()
+	if len(accel) == 0 {
+		fmt.Println("accel: (none — no slaves with accel stream enabled)")
+	} else {
+		for _, s := range accel {
+			if !s.GetValid() {
+				fmt.Printf("accel client %d: no sample yet\n", s.GetClientId())
+				continue
+			}
+			fmt.Printf("accel client %d: x=%d y=%d z=%d (age %d ms)\n",
+				s.GetClientId(), s.GetX(), s.GetY(), s.GetZ(), s.GetAgeMs())
+		}
+	}
+	taps := r.GetTaps()
+	if len(taps) == 0 {
+		fmt.Println("tap: (none pending)")
+	} else {
+		for _, e := range taps {
+			fmt.Printf("tap client %d: %s (age %d ms)\n",
+				e.GetClientId(), tapKindLabel(e.GetKind()), e.GetAgeMs())
+		}
+	}
+	return nil
+}