feat: add toolbox contract shell and testkit

packages/contract/README.md

@@ -0,0 +1,21 @@
+# @add-ideas/toolbox-contract
+
+Typed, runtime-validated toolbox application manifests and catalogs, plus safe
+same-origin context discovery and URL resolution.
+
+```ts
+import {
+  loadToolboxContext,
+  parseToolboxApp,
+} from "@add-ideas/toolbox-contract";
+
+const app = parseToolboxApp(await response.json());
+const result = await loadToolboxContext();
+```
+
+See the workspace [README](https://git.add-ideas.de/zemion/toolbox-sdk#readme)
+for the v1 document formats and full API.
+
+The canonical schemas are also published at
+`@add-ideas/toolbox-contract/schemas/toolbox-app.v1.schema.json` and
+`@add-ideas/toolbox-contract/schemas/toolbox-catalog.v1.schema.json`.