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/ndef.c

@@ -1,4 +1,6 @@
-
+// Minimal NDEF parser: finds the first record in a raw tag dump and accepts
+// only a short text record, whose text becomes the node's "name,diameter"
+// identity string.
 
 #include "ndef.h"
 // Everything read here comes off an NFC tag that anyone can write, so every
@@ -11,7 +13,8 @@
         }                                                                                          \
     }
 
-ndef_message readNDEFText(unsigned char *buf, uint8_t buf_len) {
+ndef_message readNDEFText(unsigned char* buf, uint8_t buf_len)
+{
     uint16_t addr = 0;
     NDEF_MSG.success = 0;
     NDEF_MSG.payload_len = 0;
@@ -80,7 +83,7 @@ ndef_message readNDEFText(unsigned char *buf, uint8_t buf_len) {
         return NDEF_MSG;
     }
     payload_length -= lang_str_len; // Language string
-    payload_length -= 1;            // The byte that says how long the language string is
+    payload_length -= 1; // The byte that says how long the language string is
 
     NDEF_NEED((uint16_t)lang_str_len + 1);
     addr += lang_str_len;
@@ -99,10 +102,8 @@ ndef_message readNDEFText(unsigned char *buf, uint8_t buf_len) {
     NDEF_MSG.payload[payload_length] = '\0';
     NDEF_MSG.payload_len = payload_length;
 
-    #if DO_UART
-    uart_sendString(NDEF_MSG.payload);
-    uart_sendString("\n");
-    #endif
+    LOG(NDEF_MSG.payload);
+    LOG("\n");
 
     return NDEF_MSG;
 };