Add Quick Notes example plugin demonstrating core plugin surfaces

Mirrors the Bookmarks example (PAP-3575) with a company-scoped note
library: database namespace, scoped API routes, page/sidebar/widget/
settings UI slots. All 7 tests pass.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/plugins/examples/plugin-quick-notes-example/vitest.config.ts

@@ -0,0 +1,8 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    include: ["tests/**/*.spec.ts"],
+    environment: "node",
+  },
+});