Terminal tabs resolved the shell from the dsh process environment only,
falling back to a hardcoded /bin/bash — service-managed launches without
SHELL therefore ignored the account's login shell (e.g. zsh). They also
spawned with an empty argv, so even a resolved zsh ran as a non-login
shell and skipped ~/.zprofile.
defaultShell() now falls back to the account's login shell (passwd) after
$SHELL, and both registries spawn POSIX shells with -l so the tab behaves
like a terminal emulator (loads ~/.profile / ~/.zprofile). Windows keeps
powershell.exe with no login flag.
Fixesomdsh-dev/DSH-better-sidebar#68