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/data_model.h

@@ -10,6 +10,17 @@ enum class FaultType : uint8_t {
   TimeSync = 4
 };
 
+enum class RxRejectReason : uint8_t {
+  None = 0,
+  CrcFail = 1,
+  BadProtocol = 2,
+  WrongRole = 3,
+  WrongPayloadType = 4,
+  LengthMismatch = 5,
+  DeviceIdMismatch = 6,
+  BatchIdMismatch = 7
+};
+
 struct FaultCounters {
   uint32_t meter_read_fail;
   uint32_t decode_fail;
@@ -33,6 +44,7 @@ struct MeterData {
   uint32_t err_decode;
   uint32_t err_lora_tx;
   FaultType last_error;
+  uint8_t rx_reject_reason;
 };
 
 struct SenderStatus {
@@ -42,3 +54,4 @@ struct SenderStatus {
 };
 
 void init_device_ids(uint16_t &short_id, char *device_id, size_t device_id_len);
+const char *rx_reject_reason_text(RxRejectReason reason);

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();