test: Add gateway test configuration for end-to-end testing

- Playwright config for testing localhost gateway → VM routing
- Tests full production architecture flow
- Validates Traefik routing to remote demo VM via Tailscale

Author: Matthew Valancy

playwright.gateway-test.config.ts

@@ -0,0 +1,21 @@
+import { defineConfig, devices } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './tests/e2e',
+  testMatch: '**/demo-guest-login.spec.ts',
+  fullyParallel: false,
+  retries: 0,
+  workers: 1,
+  reporter: [['list']],
+  use: {
+    baseURL: 'http://localhost:8090',
+    trace: 'on-first-retry',
+    screenshot: 'only-on-failure',
+  },
+  projects: [
+    {
+      name: 'gateway-test',
+      use: { ...devices['Desktop Chrome'] },
+    },
+  ],
+});