Apply escapeshellarg() to the Postgres username before interpolating it
into the chown command used to fix SSL certificate ownership, matching
the handling already in place for StartMysql. This keeps the sink-side
escaping consistent across database actions, independent of upstream
input validation.
Also adjusts an assertion in DatabaseSslCredentialEscapingTest to match
the actual double-escaped output of executeInDocker, and adds Postgres
regression cases for subshell and semicolon payloads.
Add ValidationPatterns helpers for database identifiers and passwords,
apply them across database Livewire components and the API controller,
encode MongoDB init script values via json_encode, and pass the MySQL
user through escapeshellarg when generating SSL chown commands.
