Add RX reject reasons to telemetry and UI

BACKWARD-INCOMPATIBLE: MeterBatch schema bumped to v2 with err_rx_reject.
- Track and log RX reject reasons (CRC/protocol/role/payload/length/id/batch)
- Include rx_reject in sender telemetry JSON and receiver web UI
- Add lora_receive reject reason logging under SERIAL_DEBUG_MODE

include/lora_transport.h

@@ -2,6 +2,7 @@
 
 #include <Arduino.h>
 #include "config.h"
+#include "data_model.h"
 
 constexpr size_t LORA_MAX_PAYLOAD = 230;
 
@@ -19,6 +20,7 @@ struct LoraPacket {
 void lora_init();
 bool lora_send(const LoraPacket &pkt);
 bool lora_receive(LoraPacket &pkt, uint32_t timeout_ms);
+RxRejectReason lora_get_last_rx_reject_reason();
 void lora_idle();
 void lora_sleep();
 void lora_receive_continuous();