Stream slave accel via ESP-NOW with master snapshot cache.

Slaves push BMA456 samples at 16ms when enabled; the master caches per
client and exposes ACCEL_SNAPSHOT and ACCEL_STREAM over UART. goTool adds
dashboard stream controls, HTTP accel-stream routes, and an external
WebSocket API with per-connection receive/interval and slave stream commands.

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

main/proto/uart_messages.proto

@@ -22,7 +22,8 @@ enum MessageType {
   OTA_SLAVE_PROGRESS = 21;
   FIND_ME = 22;
   RESTART = 23;
-  ACCEL_READ = 24;
+  ACCEL_SNAPSHOT = 24;
+  ACCEL_STREAM = 25;
 }
 
 message UartMessage {
@@ -49,8 +50,10 @@ message UartMessage {
     EspNowFindMeResponse espnow_find_me_response = 20;
     RestartRequest restart_request = 21;
     RestartResponse restart_response = 22;
-    AccelReadRequest accel_read_request = 23;
-    AccelReadResponse accel_read_response = 24;
+    AccelSnapshotRequest accel_snapshot_request = 23;
+    AccelSnapshotResponse accel_snapshot_response = 24;
+    AccelStreamRequest accel_stream_request = 25;
+    AccelStreamResponse accel_stream_response = 26;
   }
 }
 
@@ -75,6 +78,8 @@ message ClientInfo {
   uint32 last_ping = 5;
   uint32 last_success_ping = 6;
   uint32 version = 7;
+  /** Master: ESP-NOW accel stream enabled for this slave. */
+  bool accel_stream_enabled = 8;
 }
 
 message ClientInfoResponse { 
@@ -109,14 +114,40 @@ message AccelDeadzoneResponse {
   uint32 slaves_updated = 4;
 }
 
-// Host → device: read current BMA456 accelerometer sample (raw LSB, ±2g range).
-message AccelReadRequest {}
+// Host → master: enable/disable slave accel ESP-NOW stream (~16 ms per slave).
+// write=false: read; write=true: apply. client_id 0 invalid for write (use >0 or all_clients).
+message AccelStreamRequest {
+  bool write = 1;
+  bool enable = 2;
+  uint32 client_id = 3;
+  bool all_clients = 4;
+}
 
-message AccelReadResponse {
-  bool success = 1;
-  sint32 x = 2;
-  sint32 y = 3;
-  sint32 z = 4;
+message AccelStreamResponse {
+  bool enabled = 1;
+  uint32 client_id = 2;
+  bool success = 3;
+  uint32 slaves_updated = 4;
+}
+
+// Host → master: read cached accel samples from slaves (only while stream enabled).
+// client_id 0 = all registered slaves; otherwise one slave.
+message AccelSnapshotRequest {
+  uint32 client_id = 1;
+}
+
+message AccelSample {
+  uint32 client_id = 1;
+  bool valid = 2;
+  sint32 x = 3;
+  sint32 y = 4;
+  sint32 z = 5;
+  /** Milliseconds since last ESP-NOW sample from this slave. */
+  uint32 age_ms = 6;
+}
+
+message AccelSnapshotResponse {
+  repeated AccelSample samples = 1 [(nanopb).max_count = 16];
 }
 
 message EspNowUnicastTestRequest {