feat: add shared toolbox header and appearance

packages/contract/README.md

@@ -13,6 +13,10 @@ const app = parseToolboxApp(await response.json());
 const result = await loadToolboxContext();
 ```
 
+The package also owns the versioned same-origin browser preference contract. Use
+`readToolboxPreferences()` and `writeToolboxPreferences()` to share pinned apps,
+ordering, visibility, and light/dark/system mode with the Toolbox portal.
+
 See the workspace [README](https://git.add-ideas.de/zemion/toolbox-sdk#readme)
 for the v1 document formats and full API.