Refactor firmware for clarity; no functional changes

- main.c: file-header comment describing the hardware and operation, logic
  split into named phases (sleep_until_interrupt, wake_peripheral_rails,
  take_counts_snapshot, send_wheel_counts_report, handle_minute_alarm,
  init_all_hardware); shared state renamed to say what it is and made static.
- rfm69.c: reorganized into six labeled sections; cond_1/2/3 and hash scratch
  globals replaced by a reply_acknowledges() helper with clear locals; packet
  layout and every init register write documented.
- LOG() macro (compiled out when DO_UART is off) replaces the #if DO_UART
  blocks that obscured the logic.
- Drivers: file-header comments; named RTC_REG_*/RTC_ALM_MASK_BIT constants;
  EEPROM spool scheme documented; ADC_CHANNEL_BANDGAP named; repeated pin
  if/else helpers collapsed to SET_PIN_TO().
- Removed unused globals/buffers and commented-out code; ran clang-format
  with the project style.

Register writes and radio protocol are byte-identical. Builds clean under
-Wall -Wextra on gnu17 and c23; flash 13028 -> 12830 B, static RAM
1038 -> 999 B.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YVJKatfeMJjAmuH9KYiLuv

avr_code/defines.c

@@ -1,12 +1,10 @@
 #include "defines.h"
 
- unsigned char DATA_BUFFER_65[65];
- uint8_t DATA_BUFFER_7[7];
-// uint8_t DATA_BUFFER_254[255];
- unsigned char DATA_BUFFER_20[20];
- ndef_message NDEF_MSG;
- trimmed_string_struct TRIMMED_STRING;
- identifier_results IDENTIFIER;
- tx_rx_data_struct TX_DATA;
- tx_rx_data_struct RX_DATA;
- time_struct TIME;
+unsigned char DATA_BUFFER_65[65];
+uint8_t DATA_BUFFER_7[7];
+ndef_message NDEF_MSG;
+trimmed_string_struct TRIMMED_STRING;
+identifier_results IDENTIFIER;
+tx_rx_data_struct TX_DATA;
+tx_rx_data_struct RX_DATA;
+time_struct TIME;