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/api_live_stream.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+type liveStreamAPIResponse struct {
+	Enabled bool   `json:"enabled"`
+	Success bool   `json:"success"`
+	Error   string `json:"error,omitempty"`
+}
+
+func mountLiveStreamAPI(mux *http.ServeMux, hub *wsHub) {
+	mux.HandleFunc("/api/live-stream", func(w http.ResponseWriter, r *http.Request) {
+		switch r.Method {
+		case http.MethodGet:
+			serveLiveStreamGet(w, hub)
+		case http.MethodPut:
+			serveLiveStreamPut(w, r, hub)
+		default:
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		}
+	})
+}
+
+func serveLiveStreamGet(w http.ResponseWriter, hub *wsHub) {
+	enabled := false
+	if hub != nil {
+		enabled = hub.liveStreamEnabled()
+	}
+	writeJSON(w, http.StatusOK, liveStreamAPIResponse{Enabled: enabled, Success: true})
+}
+
+func serveLiveStreamPut(w http.ResponseWriter, r *http.Request, hub *wsHub) {
+	var body struct {
+		Enable bool `json:"enable"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeJSON(w, http.StatusBadRequest, liveStreamAPIResponse{Error: "invalid JSON"})
+		return
+	}
+
+	if hub != nil {
+		hub.patchLiveStream(body.Enable)
+	}
+
+	writeJSON(w, http.StatusOK, liveStreamAPIResponse{
+		Enabled: body.Enable,
+		Success: true,
+	})
+}