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/scripts/demo-stack.sh

@@ -30,6 +30,7 @@ ensure_env() {
     fi
     # Ensure new variables exist in older env files
     grep -q '^MAILHOG_SMTP_PORT=' "$ENV_FILE" || echo "MAILHOG_SMTP_PORT=4019" >> "$ENV_FILE"
+    grep -q '^HOMEPAGE_ALLOWED_HOSTS=' "$ENV_FILE" || echo "HOMEPAGE_ALLOWED_HOSTS=*" >> "$ENV_FILE"
 }
 
 detect_user() {