[RF] Deselect a secondary CC1101 chip-select on shared-SPI boards (#2363)

Boards that carry two radios on one SPI bus need the unused radio's CS held
high, or it answers on MISO and corrupts every transfer to the radio that is
actually in use. Add an optional RF_MODULE_SECONDARY_CS: when defined, drive
that pin high before probing the CC1101.

Bench-proven on a dual-CC1101 ESP32 board where one radio is faulty and the
other is the working one: without the deselect the shared bus is unreliable;
with it, the working module probes cleanly on the first attempt and decodes
live 433 MHz sensors.

No effect on single-radio boards: the whole block compiles out unless
RF_MODULE_SECONDARY_CS is set.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

main/commonRF.cpp

@@ -76,6 +76,15 @@ void initCC1101() {
   int delayMaxMS = 500;
   bool connected = false;
 
+#    ifdef RF_MODULE_SECONDARY_CS
+  // Boards carrying two radios on one SPI bus must hold the unused radio's
+  // chip-select high, or it answers on MISO and corrupts every transfer to the
+  // radio we do use.
+  pinMode(RF_MODULE_SECONDARY_CS, OUTPUT);
+  digitalWrite(RF_MODULE_SECONDARY_CS, HIGH);
+  THEENGS_LOG_NOTICE(F("Deselected secondary radio CS on GPIO%d" CR), RF_MODULE_SECONDARY_CS);
+#    endif
+
 #    if defined(RF_CC1101_SCK) && defined(RF_CC1101_MISO) && \
         defined(RF_CC1101_MOSI) && defined(RF_CC1101_CS)
   THEENGS_LOG_TRACE(F("initCC1101 with custom SPI pins, SCK=%d, MISO=%d, MOSI=%d, CS=%d" CR), RF_CC1101_SCK, RF_CC1101_MISO, RF_CC1101_MOSI, RF_CC1101_CS);