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>

.gitignore

@@ -23,6 +23,9 @@ tmp_template.yml
 # Homepage auto-generated files
 demo/config/homepage/logs/
 demo/config/homepage/kubernetes.yaml
+demo/config/homepage/custom.css
+demo/config/homepage/custom.js
+demo/config/homepage/proxmox.yaml
 
 # Playwright
 node_modules/