A second `command` node silently overwrote the first via a scalar
Option<PathBuf>, and a second `args` node silently overwrote the first
via a plain Vec, so duplicate keys last-won instead of tripping the
exactly-one-condition rule. Track args as Option<Vec<String>> and
error immediately on a repeated command or args key.
Adds kdl_parse module with parse_server_config() that deserialises a
KDL document into ServerConfig, with full validation of name, types,
durations, and restart/stop blocks. Also derives Default on
RestartPolicy to satisfy clippy.
logaritmisk