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/m95128.h

@@ -34,8 +34,7 @@
 extern "C" {
 #endif
 
-    void
-    spi_eeprom_select(bool state);
+void spi_eeprom_select(bool state);
 void eeprom_write(uint8_t page, unsigned const char* msg, uint8_t msg_len);
 void eeprom_read(uint8_t page, unsigned char* msg, uint8_t msg_len);
 void eeprom_write_tx_data(uint8_t page, tx_rx_data_struct tx_data);