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/app/VContact.cpp

@@ -380,7 +380,7 @@ bool CompanionMesh::vcontactHandleFrame(const uint8_t *data, size_t len)
 			if (tag == 0) tag = 1;
 			sendPacketSent(MSG_SEND_SENT_DIRECT, tag, 3000);
 
-			uint8_t rsp[8 + 4 + 11 + 15 + (12 * POWER_MAX_CHANNELS) + 8];
+			uint8_t rsp[8 + MAX_PACKET_PAYLOAD - 4];  /* header + telemetry */
 			int i = 0;
 			rsp[i++] = PUSH_CODE_TELEMETRY_RESPONSE;
 			rsp[i++] = 0;  /* reserved */