feat: add toolbox contract shell and testkit

CHANGELOG.md

@@ -0,0 +1,21 @@
+# Changelog
+
+All notable changes to the independently versioned Toolbox SDK packages are
+recorded here. The packages currently share one release version.
+
+## 0.1.0 — 2026-07-20
+
+### Added
+
+- `@add-ideas/toolbox-contract` with v1 app and catalog types, published JSON
+  Schemas, strict forward-compatible runtime parsing, same-origin context
+  discovery, hydrated catalog loading, resolved URL helpers, and graceful result
+  types.
+- `@add-ideas/toolbox-shell-react` with the standalone-safe `AppShell`, built-in
+  light/dark/system theme, app metadata and privacy display, actions, toolbox
+  home, and accessible full-page app switching.
+- `@add-ideas/toolbox-testkit` with the `toolbox-check` CLI for manifest/assets,
+  unsafe-path detection, nested-prefix resource checks, and standalone/context
+  HTTP smoke tests.
+- React integration and manifest/catalog examples, Vitest/jsdom coverage, and
+  workspace build, typecheck, lint, formatting, and package scripts.