Add test script to @pascal-app/core so turbo picks up its unit tests

Without a "test" script the package was invisible to `turbo test` —
private-editor's CI runs `bun run test` (= `turbo test`), which only
walks workspace packages that declare a test runner. Mirrors mcp and
nodes which already do this.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core/package.json

@@ -59,6 +59,7 @@
   "scripts": {
     "build": "tsc --build",
     "dev": "tsc --build --watch",
+    "test": "bun test",
     "prepublishOnly": "npm run build"
   },
   "peerDependencies": {