peripherals & power: GPS fixes, poweroff/pwrmgt, upstream SensorManager telemetry

- gps: servers honour gps_enabled at boot (was lost on reboot; zc.gps_set
  upgrades older prefs to on once); sleep lock only while acquiring;
  gps off works on boards without a power line (UART sleep); UI toggles
  and fixes handled on the main thread; configure only after a good init;
  observer parks its GPS; one interval clamp (clampGpsInterval); one
  nav-mode knob (room servers on Air530Z now stationary); GNSS UARTE from DT
- gps: split into ZephyrGPSManager / gps_power / gps_module_cfg
  (+gps_internal.h); dead driver branches, gps_get_diag, sats_* removed
- clock: ZephyrRTCClock writes the hardware RTC itself (clkreboot now
  resets it); MESH_EVENT_RTC_SAVE gone
- power: one power-off path (zephcore_power_off, ZephyrBoard::powerOff),
  poweroff/shutdown CLI, get pwrmgt.*, crash record kept across reboot,
  battery reading cached 10 s, fuel gauge on the current API
- telemetry: upstream SensorManager + CayenneLPP (rounded to nearest),
  one builder for all roles; per-sensor channels, MCU temp always,
  guest gating and inverse mask on servers; sensor list/get/set work;
  BME280/BMP280 also probed at 0x77
- CLI: gps in upstream's form, get gps detail, gps sync

zephcore/adapters/clock/ZephyrRTCClock.cpp

@@ -3,20 +3,45 @@
  */
 
 #include "ZephyrRTCClock.h"
+#include "ZephyrRTCDiscover.h"
 #include <zephyr/kernel.h>
+#include <zephyr/devicetree.h>
 
 namespace mesh {
 
+#if DT_HAS_COMPAT_STATUS_OKAY(zephcore_rtc_i2c)
+/* One clock per build. The work reads the time when it runs, so any number
+ * of sets before it runs are one write, of the latest time. */
+static ZephyrRTCClock *s_saved_clock;
+
+static void rtc_save_work_fn(struct k_work *work)
+{
+	ARG_UNUSED(work);
+	zephcore_rtc_save(s_saved_clock->getCurrentTime());
+}
+
+static K_WORK_DEFINE(s_rtc_save_work, rtc_save_work_fn);
+#endif
+
 uint32_t ZephyrRTCClock::getCurrentTime()
 {
 	uint32_t uptime_sec = (uint32_t)(k_uptime_get() / 1000);
 	return epoch_offset + uptime_sec;
 }
 
-void ZephyrRTCClock::setCurrentTime(uint32_t time)
+void ZephyrRTCClock::seedCurrentTime(uint32_t time)
 {
 	uint32_t uptime_sec = (uint32_t)(k_uptime_get() / 1000);
 	epoch_offset = time - uptime_sec;
 }
 
+void ZephyrRTCClock::setCurrentTime(uint32_t time)
+{
+	seedCurrentTime(time);
+#if DT_HAS_COMPAT_STATUS_OKAY(zephcore_rtc_i2c)
+	s_saved_clock = this;
+	k_work_submit(&s_rtc_save_work);
+#endif
+}
+
 } /* namespace mesh */

zephcore/adapters/clock/ZephyrRTCClock.h

@@ -12,7 +12,12 @@ namespace mesh {
 class ZephyrRTCClock : public RTCClock {
 public:
 	uint32_t getCurrentTime() override;
+	/* Also written to the board's hardware RTC, if it has one, as upstream's
+	 * AutoDiscoverRTCClock does: coalesced on the system work queue, so
+	 * callers on any thread pay no I2C. */
 	void setCurrentTime(uint32_t time) override;
+	/* Boot only: the time just read from the hardware RTC, not written back. */
+	void seedCurrentTime(uint32_t time);
 
 private:
 	uint32_t epoch_offset = 0;

zephcore/adapters/clock/ZephyrRTCDiscover.h

@@ -8,9 +8,9 @@
  * present fail the probe and are skipped — like the environment sensors.
  *
  * If a present chip holds a valid time, zephcore_rtc_restore() returns it so
- * the soft clock can be seeded at boot (shown tagged "L" — local). On every
- * authoritative sync (GPS/app/CLI) the caller writes it back via
- * zephcore_rtc_save() so time survives the next power-off.
+ * the soft clock can be seeded at boot (shown tagged "L" — local). Every
+ * ZephyrRTCClock::setCurrentTime() writes it back via zephcore_rtc_save(), so
+ * time survives the next power-off.
  */
 
 #pragma once