add snr command, update docs

INSTRUCTION.md

@@ -116,6 +116,7 @@ All commands are processed in `onGroupDataRecv()`:
 | `status` | report state | `status:armed/off temp:±X.XC hall:trig/ok motion:trig/ok bat:X.XXV/USB` |
 | `ver` | build date | `build:Mon DD YYYY HH:MM:SS` |
 | `scan` | noise floor | `noise:-XXXdBm` |
+| `snr` | RSSI и SNR последнего пакета | `rssi:-78dBm snr:+6.5dB` |
 | `uptime` | device uptime | `uptime:1d 3h 15m` |
 | `kontrol <min>` | auto-status every N min | `kontrol 60 min ok` |
 | `kontrol off` | disable auto-status | `kontrol off` |
@@ -131,6 +132,8 @@ Alerts (`alert:hall`, `alert:motion`) and startup (`poweron`) are sent immediate
 
 ### Special Commands
 
+- **`snr`** — returns `rssi:-78dBm snr:+6.5dB` based on the last received packet. Uses `radio_driver.getLastRSSI()` and `pkt->getSNR()`. Stored in `last_rssi` / `last_snr` fields, updated on every `onGroupDataRecv`.
+
 - **`reboot`** — sends `rebooting` immediately (not deferred), blinks LED 5 times, then `NVIC_SystemReset()`.
 - **`uptime`** — calculates uptime from `g_boot_time` (set at boot). Format: `uptime:1d 3h 15m` (days/hours/minutes).
 - **`kontrol <min>`** — sets `g_auto_status_interval = min * 60000`. In `loop()`, when `millis() - g_last_auto_status >= interval`, sends status. Range: 1–1440 minutes.
@@ -198,7 +201,7 @@ pio run -e promicro_security -t upload
 pio device monitor -b 115200
 ```
 
-Current resource usage: RAM 8%, Flash 36.5%.
+Current resource usage: RAM 8.1%, Flash 36.8%.
 
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