chore(devices): TEMP log power-monitor telemetry headers from firmware

Firmware emits X-Prev-Awake-Ms + X-Prev-Panel-Init-Ms on each poll
so we can verify the 13.3" PIN_PWR rail-cut change isn't slowing
the panel re-init or extending the awake window. Log them with
boot-reason context via `device.poll.power_telemetry` — greppable
in `docker logs pictureframe-php-1`. Remove this log + the
firmware NVS_KEY_PREV_* writes once the change is validated.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/Controller/DeviceImageController.php

@@ -90,6 +90,22 @@ class DeviceImageController extends AbstractController
         $currentImageId = (int) $request->headers->get('X-Current-Image-Id', '-1');
         $device->markSeen();
 
+        // TEMP: power-monitor — surface the firmware's previous-cycle
+        // telemetry (awake duration + panel-init time) so we can see
+        // whether the PIN_PWR rail cut affects either. Logged on every
+        // poll; greppable via `device.poll.power_telemetry`. Remove
+        // alongside the firmware's NVS_KEY_PREV_* writes once validated.
+        $prevAwakeMs     = $request->headers->get('X-Prev-Awake-Ms');
+        $prevPanelInitMs = $request->headers->get('X-Prev-Panel-Init-Ms');
+        if ($prevAwakeMs !== null || $prevPanelInitMs !== null) {
+            $this->logger->info('device.poll.power_telemetry', [
+                'mac'                => $mac,
+                'prev_awake_ms'      => $prevAwakeMs,
+                'prev_panel_init_ms' => $prevPanelInitMs,
+                'boot_reason'        => $request->headers->get('X-Boot-Reason'),
+            ]);
+        }
+
         // Auto-correct Device.model from the firmware's X-Panel-Id header. New
         // Devices are created with the default V1 model (see Device entity), so
         // a freshly-claimed 13.3" unit ends up wrongly flagged until its first