fix(demo): add HOMEPAGE_ALLOWED_HOSTS, harden Playwright tests

- Set HOMEPAGE_ALLOWED_HOSTS=* so Homepage accepts requests from
  localhost, LAN IPs, and Tailscale FQDNs (appropriate for demo)
- Add host validation to docker-compose.yml.template and demo.env.template
- Bootstrap HOMEPAGE_ALLOWED_HOSTS in ensure_env() for existing installs
- Harden Playwright tests: check for "host validation failed" and
  "internal server error" text, verify page titles, use stronger
  content assertions based on actual rendered content
- Pin @playwright/test to exact 1.52.0 (no caret) to prevent npm
  resolving to a version incompatible with the Docker image
- Gitignore additional Homepage auto-generated files (custom.css/js,
  proxmox.yaml)

💘 Generated with Crush

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

demo/tests/e2e/package.json

@@ -3,6 +3,6 @@
   "version": "1.0.0",
   "private": true,
   "devDependencies": {
-    "@playwright/test": "^1.52.0"
+    "@playwright/test": "1.52.0"
   }
 }