Address PR review feedback for Ethernet support

- Add #pragma once to SerialEthernetInterface.h
- Rename TCP_PORT to ETH_TCP_PORT with #ifndef guard
- Fix typos: "initalizing" → "initializing"
- Fix #elif without condition → #else for STM32 block
- Replace infinite loop on ETH init failure with halt()
- Remove heartbeat Serial.print(".") output
- Remove dead beginETH() call (ETH_ENABLED, not RAK_ETH_ENABLE)
- Comment out MESH_DEBUG and ETH_DEBUG_LOGGING build flags

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

examples/companion_radio/main.cpp

@@ -12,7 +12,6 @@ static uint32_t _atoi(const char* sp) {
   return n;
 }
 
-uint32_t tick_count = 0;
 
 #if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
   #include <InternalFileSystem.h>
@@ -87,7 +86,7 @@ uint32_t tick_count = 0;
   #ifdef ETH_ENABLED
     #include <helpers/nrf52/SerialEthernetInterface.h>
     SerialEthernetInterface serial_interface;
-  #elif
+  #else
     #include <helpers/ArduinoSerialInterface.h>
     ArduinoSerialInterface serial_interface;
   #endif
@@ -161,7 +160,7 @@ void setup() {
 
 #ifdef BLE_PIN_CODE
   serial_interface.begin(BLE_NAME_PREFIX, the_mesh.getNodePrefs()->node_name, the_mesh.getBLEPin());
-#elif ETH_ENABLED
+#elif defined(ETH_ENABLED)
 
   Serial.print("Waiting for serial to connect...\n");
   time_t timeout = millis();
@@ -170,13 +169,11 @@ void setup() {
   {
     if ((millis() - timeout) < 5000) { delay(100); } else { break; }
   }
-  Serial.print("Initalizing ethernet adapter....\n");
+  Serial.print("Initializing ethernet adapter....\n");
   bool result = serial_interface.begin();
   if (!result) {
-    while (true)
-      {
-        delay(1); // Do nothing, just love you.
-      }
+    Serial.println("ETH: Init failed, halting");
+    halt();
   }
 #else
   serial_interface.begin(Serial);
@@ -252,12 +249,6 @@ void loop() {
 #endif
   rtc_clock.tick();
 
-  // Debugging only... making sure something is alive.
-  tick_count++;
-  if (tick_count % 5000 == 0) {
-    Serial.print(".");
-  }
-
 #ifdef ETH_ENABLED
   serial_interface.maintain();
 #endif