Add plugin framework and settings UI

packages/plugins/examples/plugin-hello-world-example/README.md

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+# @paperclipai/plugin-hello-world-example
+
+First-party reference plugin showing the smallest possible UI extension.
+
+## What It Demonstrates
+
+- a manifest with a `dashboardWidget` UI slot
+- `entrypoints.ui` wiring for plugin UI bundles
+- a minimal React widget rendered in the Paperclip dashboard
+- reading host context (`companyId`) from `PluginWidgetProps`
+- worker lifecycle hooks (`setup`, `onHealth`) for basic runtime observability
+
+## API Surface
+
+- This example does not add custom HTTP endpoints.
+- The widget is discovered/rendered through host-managed plugin APIs (for example `GET /api/plugins/ui-contributions`).
+
+## Notes
+
+This is intentionally simple and is designed as the quickest "hello world" starting point for UI plugin authors.
+It is a repo-local example plugin for development, not a plugin that should be assumed to ship in generic production builds.
+
+## Local Install (Dev)
+
+From the repo root, build the plugin and install it by local path:
+
+```bash
+pnpm --filter @paperclipai/plugin-hello-world-example build
+pnpm paperclipai plugin install ./packages/plugins/examples/plugin-hello-world-example
+```
+
+**Local development notes:**
+
+- **Build first.** The host resolves the worker from the manifest `entrypoints.worker` (e.g. `./dist/worker.js`). Run `pnpm build` in the plugin directory before installing so the worker file exists.
+- **Dev-only install path.** This local-path install flow assumes a source checkout with this example package present on disk. For deployed installs, publish an npm package instead of relying on the monorepo example path.
+- **Reinstall after pulling.** If you installed a plugin by local path before the server stored `package_path`, the plugin may show status **error** (worker not found). Uninstall and install again so the server persists the path and can activate the plugin:  
+  `pnpm paperclipai plugin uninstall paperclip.hello-world-example --force` then  
+  `pnpm paperclipai plugin install ./packages/plugins/examples/plugin-hello-world-example`.