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)

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

demo/docker-compose.yml.template

@@ -94,6 +94,7 @@ services:
     volumes:
       - ./config/homepage:/app/config
     environment:
+      - HOMEPAGE_ALLOWED_HOSTS=${HOMEPAGE_ALLOWED_HOSTS}
       - PUID=${DEMO_UID}
       - PGID=${DEMO_GID}
     labels: