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/HalTiltSensor.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <Arduino.h>
+#include <Imu.h>
 #include <Wire.h>
 
 #include "HalGPIO.h"
@@ -18,8 +19,12 @@ class HalTiltSensor;
 extern HalTiltSensor halTiltSensor;  // Singleton
 
 class HalTiltSensor {
+  enum class Backend : uint8_t { None, Qmi8658, SdkImu };
+
   bool _available = false;
+  Backend _backend = Backend::None;
   uint8_t _i2cAddr = 0;
+  mutable Imu _sdkImu;
 
   // Tilt gesture state machine
   bool _tiltForwardEvent = false;  // Consumed by wasTiltedForward()