M3 step 1: RadioLib and lora probe

The probe finds the SX1262 (TCXO 1.8 V works) and measures the antenna
path: the Cap's PI4IOE5V6408 at 0x43 must drive P0 high, or the receiver
is deaf (-111.9 dBm flat vs -87 to -94 dBm with P0 high). DIO2 makes no
difference to reception. Receive only; the radio is left asleep.

RadioLib 7.8.1 + probe: +23.6 KB flash, +656 B static RAM (release).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/platform/pins.h

@@ -14,4 +14,9 @@ constexpr int kSpiMosi = 14;
 constexpr int kSdCs = 12;
 constexpr int kLoraCs = 5;
 
+// The SX1262 on the Cap (as in Meshtastic's board file for the Cardputer ADV).
+constexpr int kLoraReset = 3;
+constexpr int kLoraIrq = 4;  // DIO1
+constexpr int kLoraBusy = 6;
+
 }  // namespace roro::pins