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.

ROADMAP.md

@@ -8,14 +8,18 @@
 - [x] List firmware modification ideas with priorities
 - [x] Verify build from repo (ESP-IDF v5.5.2, aarch64)
 
-## v0.2 - Remote Management
-- [ ] Add UDP command listener on ESP32
-- [ ] Implement REBOOT command
-- [ ] Implement IDENTIFY command (blink LED)
-- [ ] Implement STATUS command (uptime, heap, RSSI, temp)
-- [ ] Implement RATE command (change sampling rate)
-- [ ] Add LED status indicator (connected/sending/error)
-- [ ] Pi-side command sender script
+## v0.2 - Remote Management [IN PROGRESS]
+- [x] Add UDP command listener on ESP32 (port 5501)
+- [x] Implement REBOOT command
+- [x] Implement IDENTIFY command (LED solid 5s)
+- [x] Implement STATUS command (uptime, heap, RSSI, tx_power, rate)
+- [x] Implement RATE command (change ping Hz, NVS persist)
+- [x] Implement POWER command (TX power dBm, NVS persist)
+- [x] Add LED status indicator (off/slow blink/fast blink/solid)
+- [x] NVS persistence for rate and tx_power settings
+- [x] Pi-side `esp-cmd` CLI tool
+- [ ] Build and flash test on device
+- [ ] Update CHEATSHEET.md with new commands
 
 ## v0.3 - OTA Updates
 - [ ] Modify partition table for dual OTA