pub fn default_atomcode_dir() -> PathBufExpand description
Return the AtomCode data directory, respecting the ATOMCODE_HOME
environment variable. When ATOMCODE_HOME is set, it IS the data root
(no .atomcode suffix is appended). Otherwise falls back to
$HOME/.atomcode, or ./.atomcode when $HOME cannot be resolved.
This mirrors the logic in atomcode_core::config::Config::config_dir()
but is implemented independently to avoid a circular dependency between
the atomcode-telemetry and atomcode-core crates.