fix(docker): ship a static welcome page instead of phpinfo() (#2524)
The default /app/public/index.php ran phpinfo(). Derived images without their own index served it verbatim, exposing environment variables, php.ini directives, versions and paths. Reuse the RPM/deb welcome page (package/content/index.php) as the single default index across Docker, RPM and deb. The page discloses nothing. See GHSA-cj57-c655-p798.
Welcome page graphic design by @ginifizz.
Co-authored-by: ginifizz <16579730+ginifizz@users.noreply.github.com>