docs: note SIM868 RTC set via AT+CCLK (BUG-18 follow-up)

BUGS.md

@@ -39,8 +39,11 @@ When CLOSED, move the entire entry to Resolved — don't duplicate.
 - **Verification**: DS3231 probes at `0x68` (`UU`), its 24C32 EEPROM at `0x57`, `/dev/rtc0`
   registered. Power-cycle test passed — after a full unplug/replug the boot log reads
   `setting system clock to 2026-08-14…` from the RTC (was `2000-01-01` before), and
-  `hwclock -r` matches system time. (Debugging note: the first scans were an empty bus due to
-  a data-line wiring issue, resolved during re-soldering.)
+  `hwclock -r` matches system time; the `SET TIME!` recovery line no longer appears (stable
+  oscillator on CR2032). (Debugging note: the first scans were an empty bus due to a data-line
+  wiring issue, resolved during re-soldering.) SIM868 HAT RTC was also set to the correct time
+  via `AT+CCLK` (was factory-default 2004) — its CR1220 hold will be confirmed on the next
+  power cycle.
 
 ### BUG-17 — Server trip timestamps wrong after an offline period
 - **Status**: `CLOSED` 2026-08-14