feat: Add v0.2 remote management — UDP commands, LED, NVS persistence

Firmware (app_main.c):
- UDP command listener on port 5501 (configurable via Kconfig)
- Commands: REBOOT, IDENTIFY, STATUS, RATE, POWER
- LED status indicator on GPIO2 (off/slow/fast blink/solid)
- NVS persistence for send_rate and tx_power settings
- Refactored ping to support stop/restart for dynamic rate changes
- TX power control via esp_wifi_set_max_tx_power()

Pi-side tooling:
- tools/esp-cmd: standalone Python3 UDP client for device management

Tested on amber-maple (ESP32 v3.1) with ESP-IDF v5.5.2.

get-started/csi_recv_router/main/Kconfig.projbuild

@@ -13,4 +13,11 @@ menu "CSI UDP Configuration"
         help
             UDP port on the target host for receiving CSI data.
 
+    config CSI_CMD_PORT
+        int "Command listener UDP port"
+        default 5501
+        range 1024 65535
+        help
+            UDP port for receiving management commands (STATUS, REBOOT, etc.).
+
 endmenu