test: E2E smoke tests + Playwright browser tests (23 tests)

smoke.sh:
- Full E2E smoke test: health, npm proxy/publish/security, Maven, PyPI, Docker, Raw, UI, mirror CLI
- Self-contained: starts NORA, runs tests, cleans up

Playwright (tests/e2e/):
- Dashboard: page load, registry sections visible, npm count > 0, Docker stats
- npm: URL rewriting, scoped packages, tarball download, publish, immutability, security
- Docker: v2 check, catalog, manifest push/pull, tags list
- Maven: proxy download, upload
- PyPI: simple index, package page
- Raw: upload and download
- Health, metrics, OpenAPI endpoints

All 23 tests pass in 4.7s against live NORA instance.

tests/e2e/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "nora-e2e",
+  "private": true,
+  "scripts": {
+    "test": "npx playwright test",
+    "test:ui": "npx playwright test --ui"
+  },
+  "devDependencies": {
+    "@playwright/test": "^1.50.0"
+  }
+}