Let OWE own video backgrounds while it runs

The background plugin now watches for the OWE daemon socket. While OWE is
running, the desktop yields video playback to it and the shell keeps
stills. The lock screen keeps its own playback.

This lets Omarchy cooperate with OWE without OWE editing shell.json, so
the engine can ship as a package.

Add a package-list note that owe-wallpaper-engine must be added once it is
packaged.

shell/Ui/BackgroundMedia.qml

@@ -8,6 +8,10 @@ Item {
   property int version: 0
   property bool playbackEnabled: true
   property bool audioEnabled: false
+  // The desktop yields video playback to OWE while it runs, so two engines
+  // never decode the same file. The lock screen leaves this off and keeps its
+  // own playback.
+  property bool deferVideo: false
   // Bumped when the file behind an unchanged path may have been replaced.
   // Images cache-bust through version; a video is rebuilt, since FFmpeg
   // would read a query as part of the filename.
@@ -37,7 +41,7 @@ Item {
   Loader {
     id: videoLoader
     anchors.fill: parent
-    active: root.path !== "" && root.video && !root.reloading
+    active: root.path !== "" && root.video && !root.reloading && !root.deferVideo
     source: "BackgroundVideo.qml"
   }
 

shell/plugins/background/Background.qml

@@ -32,6 +32,25 @@ Item {
   // services so playback can stop whenever nothing can see the wallpaper.
   property var shell: null
 
+  // When the OWE wallpaper engine is running, it owns video backgrounds. This
+  // plugin keeps stills, which OWE hands back to it, and the lock screen keeps
+  // its own playback.
+  property bool oweActive: false
+
+  Process {
+    id: oweStatusProc
+    command: ["bash", "-c", "test -S \"${XDG_RUNTIME_DIR:-/run/user/$(id -u)}/owe/owed.sock\""]
+    onExited: root.oweActive = (exitCode === 0)
+  }
+
+  Timer {
+    id: oweStatusTimer
+    interval: 5000
+    repeat: true
+    running: true
+    onTriggered: if (!oweStatusProc.running) oweStatusProc.running = true
+  }
+
   // Stop a video wallpaper's decoding whenever it is covered. Qt's FFmpeg
   // engine drives its own clock, so an unseen player keeps decoding until it
   // is told not to — a locked laptop would otherwise decode until it died.
@@ -204,7 +223,10 @@ Item {
     }
   }
 
-  Component.onCompleted: refreshBackground()
+  Component.onCompleted: {
+    oweStatusProc.running = true
+    refreshBackground()
+  }
 
   Variants {
     model: Quickshell.screens
@@ -264,6 +286,7 @@ Item {
         anchors.fill: parent
         path: root.displayedBackground
         reloads: root.displayedReloads
+        deferVideo: root.oweActive
         playbackEnabled: !root.sessionObscured && !root.powerSaverActive && !panel.fullscreenHere
         audioEnabled: panel.firstScreen
         onReadyChanged: {