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/spi.c

@@ -1,26 +1,18 @@
 
 #include "spi.h"
 
-
-
+// RFM69 chip select (SS1/PE2, active low)
 void spi_rfm69_select(bool state)
 {
     SET_PIN_OUT(DDRE, DDE2);
-    if (!state) {
-        SET_PIN_HIGH(PORTE, PE2);
-    } else {
-        SET_PIN_LOW(PORTE, PE2);
-    }
+    SET_PIN_TO(PORTE, PE2, !state);
 }
 
+uint8_t spi_write(uint8_t data)
+{
+    SPDR1 = data; // Load data into the SPI data register
+    while (!(SPSR1 & (1 << SPIF1))) { }; // Wait for transmission to complete
+    return SPDR1; // Return received data
+}
 
-    uint8_t spi_write(uint8_t data) {
-        SPDR1 = data; // Load data into the SPI data register
-        while (!(SPSR1 & (1 << SPIF1))) {
-        }; // Wait for transmission to complete
-        return SPDR1; // Return received data
-    }
-
-    uint8_t spi_read(void) {
-        return spi_write(0xFF);
-    }
+uint8_t spi_read(void) { return spi_write(0xFF); }