Promote shell to its own top-level directory

shell/plugins/background/manifest.json

@@ -0,0 +1,11 @@
+{
+  "schemaVersion": 1,
+  "id": "omarchy.background",
+  "name": "Background",
+  "version": "1.0.0",
+  "author": "Omarchy",
+  "description": "Desktop background renderer with click handling and transitions",
+  "kinds": ["service"],
+  "activation": "startup",
+  "entryPoints": { "service": "Background.qml" }
+}