Move gateway management functions (gateway_status, gateway_info,
gateway_add, gateway_select, gateway_login, gateway_logout, gateway_list,
gateway_remove, gateway_use, gateway_info_not_configured) and their
private helpers from run.rs into commands/gateway.rs. Add pub use
re-exports in run.rs so main.rs call sites remain unchanged.
Extract shared test utilities (EnvVarGuard, with_tmp_xdg) into a
crate-level test_utils module to avoid duplication between gateway
tests and the remaining run.rs tests.
Part of #2304 (PR 2/6).
Signed-off-by: Varsha Prasad Narsing <varshaprasad96@gmail.com>
Drew Newberry