fix: GPS shutdown active-level, buzzer octave-8 consistency, waypoint header read checks

- UITask::shutdown(): power GPS off using !PIN_GPS_EN_ACTIVE instead of hardcoded
  LOW, matching MicroNMEALocationProvider::stop() (still LOW on current active-high
  devices, but correct for a future active-low GPS).
- buzzer _noteFreq(): clamp octave to 8 instead of 7 so the parser's accepted range
  (4-8) is fully consumed; previously an octave-8 digit was clamped away and could
  leak into the stream as the next note's duration.
- Waypoint::readFrom(): check read() return for version/reserved/count header bytes
  so a truncated file is rejected instead of using garbage count.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.cpp

@@ -1523,8 +1523,12 @@ void UITask::shutdown(bool restart){
     // Power off GPS before SYSTEMOFF — GPIO pins retain state in NRF52 SYSTEMOFF,
     // so without this the GPS stays powered and drains the battery.
     // gps_enabled is already persisted to flash; applyGpsPrefs() restores it on next boot.
+    // Use the same active level as MicroNMEALocationProvider::stop() (default active-high).
+    #ifndef PIN_GPS_EN_ACTIVE
+      #define PIN_GPS_EN_ACTIVE HIGH
+    #endif
     pinMode(PIN_GPS_EN, OUTPUT);
-    digitalWrite(PIN_GPS_EN, LOW);
+    digitalWrite(PIN_GPS_EN, !PIN_GPS_EN_ACTIVE);
 #endif
     _board->powerOff();
   }