Add per-slave ESP-NOW OTA progress over UART and fix dashboard updates.

Expose OTA_SLAVE_PROGRESS on the master, track per-slave state during
distribution, run ESP-NOW OTA in a background task so the host can poll
while slaves update, and show master/slave progress in the dashboard
with table layout and faster WebSocket refresh during uploads.

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

main/CMakeLists.txt

@@ -20,6 +20,7 @@ idf_component_register(
   "cmd_accel_deadzone.c"
   "cmd_espnow_unicast_test.c"
   "cmd_ota.c"
+  "cmd_ota_slave_progress.c"
   "ota_uart.c"
   "ota_espnow.c"
   "client_registry.c"