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.c

@@ -1,16 +1,21 @@
+// M95128 SPI EEPROM used as a LIFO spool for unacknowledged radio packets.
+//
+//   Page 0, byte 0:  depth of the spool (the highest page currently in use;
+//                    0 means empty)
+//   Pages 1..N:      one 64-byte packet each -- 60 msg bytes followed by
+//                    flags, from, to, dtype
+//
+// write_struct_to_last_page() pushes, read_struct_last_page() peeks, and
+// delete_last_page() pops.
+
 #include "m95128.h"
 
 uint8_t read_value;
-uint8_t old_last_page;
-uint8_t new_last_page;
+// EEPROM chip select (PB0, active low)
 void spi_eeprom_select(bool state)
 {
     SET_PIN_OUT(DDRB, DDB0);
-    if (!state) {
-        SET_PIN_HIGH(PORTB, PB0);
-    } else {
-        SET_PIN_LOW(PORTB, PB0);
-    }
+    SET_PIN_TO(PORTB, PB0, !state);
 }
 
 void eeprom_write(uint8_t page, unsigned const char* msg, uint8_t msg_len)
@@ -68,13 +73,12 @@ void eeprom_read(uint8_t page, unsigned char* msg, uint8_t msg_len)
 
 void delete_last_page(void)
 {
-    old_last_page = get_last_page();
+    uint8_t old_last_page = get_last_page();
     if (old_last_page == 0) // If we have nothing, no need to delete anything
     {
         return;
     }
-    new_last_page = old_last_page - 1;
-    write_last_page_value(new_last_page);
+    write_last_page_value(old_last_page - 1);
     eeprom_clear_page(old_last_page);
 }