feat(rotation): X-Boot-Reason: cold forces a resync regardless of schedule

Cold-boot polls (firmware sends X-Boot-Reason: cold on UNDEFINED
wakeup cause) are treated as a deliberate "force a refresh" gesture
from the user — unplug → replug to re-pull whatever the web app
queued. Timer wakes still respect the wakeTimes schedule, so the
schedule-gated semantics aren't undermined.

Test: a cold-boot poll between scheduled wake times advances the
rotation and writes a fresh DeviceImageHistory row, while an
otherwise-identical timer-wake poll returns 304 without rotating.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Controller/DeviceImageController.php

@@ -83,14 +83,18 @@ class DeviceImageController extends AbstractController
         // the second flush triggers a second publish to keep it accurate.
         $this->mercure->publishDevice((int) $device->getId(), $this->serializer->serialize($device));
 
-        // Locked image bypasses rotation entirely. Otherwise, only advance the
-        // rotation when the device's configured schedule says it's due —
-        // off-schedule polls (boot, button-mash, scheduler-driven status check)
-        // hand back the device's current image without rotating, so the user
-        // doesn't see surprise refreshes between configured wake times.
+        // Locked image bypasses rotation entirely. Otherwise, advance only
+        // when the device's configured schedule says it's due — except a
+        // cold-boot poll (X-Boot-Reason: cold) is treated as a deliberate
+        // user-driven force-refresh: unplug → replug → fresh rotation,
+        // regardless of wakeTimes. Timer wakes stay schedule-gated, so users
+        // don't see surprise refreshes between configured slots.
+        $bootReason = strtolower((string) $request->headers->get('X-Boot-Reason', ''));
+        $forceResync = ($bootReason === 'cold');
+
         if ($device->getLockedImage() !== null) {
             $image = $device->getLockedImage();
-        } elseif ($this->rotation->isDue($device)) {
+        } elseif ($forceResync || $this->rotation->isDue($device)) {
             $image = $this->rotation->advance($device);
         } else {
             $image = $device->getCurrentImage();