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

src/payload_codec.h

@@ -13,6 +13,7 @@ struct BatchInput {
   uint8_t err_d;
   uint8_t err_tx;
   uint8_t err_last;
+  uint8_t err_rx_reject;
   uint32_t energy_wh[30];
   int16_t p1_w[30];
   int16_t p2_w[30];