feat(demo): add Playwright browser tests, fix Homepage config mount

- Add Playwright E2E test suite covering all 13 user-facing services
- Fix Homepage HTTP 500 by removing read-only bind mount (:ro) so it
  can create its required logs/ directory
- Pin @playwright/test to exact 1.52.0 to match Docker image browsers
- Add .gitignore entries for auto-generated Homepage files and
  Playwright artifacts
- All 13 Playwright tests passing (Chromium headless)

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

demo/tests/e2e/playwright.config.ts

@@ -0,0 +1,21 @@
+import { defineConfig } from '@playwright/test';
+
+export default defineConfig({
+  testDir: '.',
+  testMatch: '*.spec.ts',
+  timeout: 60000,
+  retries: 1,
+  use: {
+    headless: true,
+    browserName: 'chromium',
+    launchOptions: {
+      args: ['--no-sandbox', '--disable-setuid-sandbox'],
+    },
+  },
+  projects: [
+    {
+      name: 'chromium',
+      use: { browserName: 'chromium' },
+    },
+  ],
+});