Move the Nano link to Serial2, update READMEs

- ESP32 talks to the Nano on UART2 (GPIO 17 TX / GPIO 16 RX); Serial (USB)
  is now free for debug output and boot messages no longer reach the Nano
- README: wiring table, actual schedule (clock from 08:00), TODO section
  for the rewiring

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/esp32/main.cpp

@@ -14,9 +14,9 @@ void waitForNano()
   uint32_t start = millis();
   while (millis() - start < NANO_BOOT_TIMEOUT)
   {
-    while (Serial.available())
+    while (nanoSerial.available())
     {
-      char c = Serial.read();
+      char c = nanoSerial.read();
       if (c == '\n')
       {
         line[len] = '\0';
@@ -39,10 +39,10 @@ void relayOn()
   if (relay_on)
     return;
 
-  Serial.begin(115200);
+  nanoSerial.begin(115200, SERIAL_8N1, nano_rx, nano_tx);
   // drop old data (e.g. ERR replies) so only a new READY counts
-  while (Serial.available())
-    Serial.read();
+  while (nanoSerial.available())
+    nanoSerial.read();
 
   digitalWrite(relay, LOW);
   waitForNano();
@@ -55,8 +55,8 @@ void relayOff()
   relay_on = false;
 
   // An idle UART TX line is high and would power the Nano through its RX pin
-  Serial.flush();
-  Serial.end();
+  nanoSerial.flush();
+  nanoSerial.end();
   pinMode(nano_tx, INPUT);
 }
 void turnPowerOff(uint32_t delay = 30000, bool _turn_hassio_power_off = false)
@@ -289,7 +289,7 @@ void setup()
   pinMode(relay, OUTPUT);
   relayOn();
 
-  display.begin(&Serial);
+  display.begin(&nanoSerial);
   // display.setTiming(200);
   // display.setTiming(180);
   // display.setTiming(220); // works best so far