Add SDK RTC and IMU hardware abstraction support

Integrate SDK-based RTC and IMU backends as alternatives to direct hardware access. HalClock now attempts SDK RTC initialization and caches time values for reliability. HalTiltSensor adds SDK IMU backend with fallback logic. ClockOffsetActivity gains touch and swipe gesture support for field navigation.

lib/hal/HalClock.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <Arduino.h>
+#include <Rtc.h>
 #include <Wire.h>
 
 #include "HalGPIO.h"
@@ -10,6 +11,8 @@ extern HalClock halClock;  // Singleton
 
 class HalClock {
   bool _available = false;
+  bool _usesSdkRtc = false;
+  mutable Rtc _sdkRtc;
   mutable uint8_t _cachedHour = 0;
   mutable uint8_t _cachedMinute = 0;
   mutable bool _hasCachedTime = false;