fix(firmware): accept WPA/WPA2-mixed routers; warn about compact-board thermal risk

Lower the STA auth threshold from WPA2_PSK to WPA_PSK so routers running
WPA/WPA2-mixed compatibility mode aren't rejected with
WIFI_REASON_NO_AP_FOUND_IN_AUTHMODE_THRESHOLD (reason=211), and log the
disconnect reason/rssi instead of retrying blind. Also document the thermal
risk of running this firmware's continuous-radio, tier-2 DSP pipeline on
coin-sized clone boards (ESP32-S3-Zero, SuperMini) with minimal PCB copper
and budget regulators, after a field report of three such boards failing to
power on following a normal session.

Co-Authored-By: claude-flow <ruv@ruv.net>

firmware/esp32-csi-node/README.md

@@ -113,6 +113,8 @@ curl http://<ESP32_IP>:8032/wasm/list
 
 > **Tip:** A single node provides presence and vital signs along its line of sight. Multiple nodes (3-6) create a multistatic mesh that resolves 3D pose with <30 mm jitter and zero identity swaps.
 
+> **⚠️ Thermal warning — compact boards (ESP32-S3-Zero, SuperMini, other coin-sized clones):** This firmware runs the WiFi radio with modem sleep disabled (`WIFI_PS_NONE`, required for continuous CSI capture) plus a full edge-processing DSP pipeline on Core 1 (`edge_tier=2`) plus, on ADR-183 builds, a continuous 40 Hz onboard LED driver. That's sustained high current draw with no duty-cycling. Full-size dev boards (DevKitC-1, XIAO) have more copper pour and thermal mass around the regulator and tolerate this fine. Coin-sized clones with minimal PCB area and budget regulators may run hot to the touch during normal operation, and in at least one field report, boards that ran hot during a session failed to power on afterward (regulator damage suspected — see issue tracker). Give these boards airflow, don't stack or enclose them, and check them by touch during the first several minutes of a new deployment. If a board is uncomfortably hot (not just warm), power it down and let it cool before continuing.
+
 ---
 
 ## Firmware Architecture

firmware/esp32-csi-node/main/main.c

@@ -67,6 +67,8 @@ static void event_handler(void *arg, esp_event_base_t event_base,
     if (event_base == WIFI_EVENT && event_id == WIFI_EVENT_STA_START) {
         esp_wifi_connect();
     } else if (event_base == WIFI_EVENT && event_id == WIFI_EVENT_STA_DISCONNECTED) {
+        wifi_event_sta_disconnected_t *disc = (wifi_event_sta_disconnected_t *)event_data;
+        ESP_LOGW(TAG, "WiFi disconnected, reason=%d rssi=%d", disc->reason, disc->rssi);
         if (s_retry_num < MAX_RETRY) {
             esp_wifi_connect();
             s_retry_num++;
@@ -102,7 +104,10 @@ static void wifi_init_sta(void)
 
     wifi_config_t wifi_config = {
         .sta = {
-            .threshold.authmode = WIFI_AUTH_WPA2_PSK,
+            /* WPA_PSK (not WPA2_PSK) so routers running WPA/WPA2-mixed
+             * compatibility mode aren't rejected with
+             * WIFI_REASON_NO_AP_FOUND_IN_AUTHMODE_THRESHOLD (#1050). */
+            .threshold.authmode = WIFI_AUTH_WPA_PSK,
         },
     };