fix: review fixes for the boot pin warnings

- The backup record's fallback RX pin is 35, as the radio's default is.
- BootPins.h, pins.js and Transceiver.cpp say to keep the pins, the radio
  pins checked and the shared RX/TX rule in step.
- index.js reads the chip model through one chipModel().
- BootPins.RADIO is RADIO_PINS; the P4 test builds its config once.

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

src/ConfigRecords.h

@@ -183,7 +183,7 @@ struct trans_record_t {
   uint8_t MOSIPin = 23;
   uint8_t MISOPin = 19;
   uint8_t TXPin = 13;
-  uint8_t RXPin = 12;
+  uint8_t RXPin = 35;
   float frequency = 433.42;
   float rxBandwidth = 99.97;
   float deviation = 47.60;