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/helpers/PrefsJson.cpp

@@ -237,6 +237,7 @@ protected:
 		def("tz_offset", _p->tz_offset);
 		def("backoff", _p->backoff_multiplier);
 		def("disc_ts", _p->discovery_mod_timestamp);
+		def("gps_set", _p->gps_enabled_set);
 	}
 
 public:
@@ -329,9 +330,17 @@ bool serverPrefsFromJson(NodePrefs &p, Stream &in)
 	NodePrefs t = p;
 	ServerJson j(&t);
 
+	/* Absent keys keep the caller's value, so clear the marker first: a
+	 * file from before it existed was written by firmware that ran the GPS
+	 * regardless of gps.en, and keeps doing so (NodePrefs.h). */
+	t.gps_enabled_set = 0;
 	if (!j.load(in)) {
 		return false;
 	}
+	if (!t.gps_enabled_set) {
+		t.gps_enabled = 1;
+		t.gps_enabled_set = 1;
+	}
 	saneRadio(t);
 	sanitizeNodePrefs(&t);
 	p = t;