fix(home): preview tracks frame state even with locked images and 304 polls

Three problems were stacked:

1. The 200 serving path didn't set currentImage when a locked image was
   served (RotationService.advance bypassed). The frame got the locked
   photo; the DB kept the previous one; Home showed the old one.

2. The 304 path didn't flush at all. lastSeenAt (markSeen) was lost on
   every no-change poll, and any drift in currentImage couldn't self-heal.
   For a frame that's been locked for a while, polls cycle as 304 forever
   and the DB stays wrong indefinitely.

3. Pull-to-refresh fetched via fetchDevices(), which flips loading=true
   and replaces the cards with "Loading…" mid-fetch. The PTR spinner was
   working but users couldn't see the result of their refresh.

Fixes:
- Both 200 and 304 paths now set currentImage = $image and flush. The
  304 path becomes self-healing for any device whose currentImage drifted
  from reality (e.g., from before the 200-path fix).
- fetchDevices / fetchImages take an optional { silent: true } that
  skips toggling loading.value. PTR refresh callbacks pass silent so
  the cards stay visible during background refresh.
- HomeView also listens on visibilitychange and silently re-fetches when
  the PWA returns to foreground, so reopening the app shows current
  state without a manual pull.

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

src/Controller/DeviceImageController.php

@@ -100,6 +100,16 @@ class DeviceImageController extends AbstractController
             && $device->getCurrentImageOrientation() === $device->getOrientation()
             && $renderedAt !== null
             && $device->getCurrentRenderedAt()?->getTimestamp() === $renderedAt->getTimestamp()) {
+            // Self-heal currentImage: locked-image polls bypass advance() which
+            // would otherwise have set this. Without the assignment, currentImage
+            // stays stale — Home would keep showing the previous photo even
+            // though the device has been confirming the new one for cycles.
+            // Also flush so markSeen() above is persisted on every 304 (lastSeenAt
+            // would otherwise freeze whenever the device polls and gets no
+            // change, causing the status badge to drift to "offline").
+            $device->setCurrentImage($image);
+            $em->flush();
+
             $this->logger->info('device.poll.no_change', [
                 'device_id'   => $device->getId(),
                 'mac'         => $mac,
@@ -125,8 +135,16 @@ class DeviceImageController extends AbstractController
             return $r;
         }
 
-        // Record the orientation and rendered_at we're serving at so the next
-        // poll's 304 check can detect a flip or a re-render and force a re-fetch.
+        // Record what the device is now showing, plus the orientation and
+        // rendered_at we served at (so the next 304 check can detect a flip
+        // or a re-render and force a re-fetch).
+        //
+        // currentImage must be set here for the locked-image path: rotation
+        // is bypassed when a lock is in effect, so RotationService.advance()
+        // never runs to update currentImage. Without this assignment, Home
+        // would keep showing the previous photo even after the device pulled
+        // the locked one.
+        $device->setCurrentImage($image);
         $device->setCurrentImageOrientation($device->getOrientation());
         $device->setCurrentRenderedAt($renderedAt);
         $em->flush();