feat(wallpaper): add apply_wallpaper workflow and rotation worker

Adds a new apply_wallpaper command and its plumbing across
desktop, mobile, and Android. A WorkManager-based rotation
worker handles applying wallpapers in the background. Wallpaper
state now tracks currentId and imageIds for precise control.

- Introduced apply_wallpaper command across desktop, mobile and Android
- Added WorkManager-based rotation worker to apply wallpapers in the
  background
- Extended wallpaper state with currentId and imageIds and updated schemas/permissions

plugins/android/src/main/java/WallpaperRotationWorker.kt

@@ -0,0 +1,28 @@
+package de.wechselbild.wallpaper
+
+import android.content.Context
+import androidx.work.ExistingWorkPolicy
+import androidx.work.OneTimeWorkRequestBuilder
+import androidx.work.WorkManager
+import androidx.work.Worker
+import androidx.work.WorkerParameters
+
+class WallpaperRotationWorker(context: Context, parameters: WorkerParameters) : Worker(context, parameters) {
+  override fun doWork(): Result {
+    if (!WallpaperStore.enabled(applicationContext)) return Result.success()
+    if (WallpaperStore.applyNext(applicationContext)) return Result.success()
+    return if (runAttemptCount < 2) Result.retry() else Result.failure()
+  }
+
+  companion object {
+    private const val WORK_NAME = "wallpaper-rotation"
+
+    fun enqueue(context: Context) {
+      WorkManager.getInstance(context).enqueueUniqueWork(
+        WORK_NAME,
+        ExistingWorkPolicy.KEEP,
+        OneTimeWorkRequestBuilder<WallpaperRotationWorker>().build(),
+      )
+    }
+  }
+}