feat(suspend): hold inhibit lock while any zellij session exists

The SSH-shell inhibitor in dot_zprofile is bound to the lifetime of the
login shell, so it disappears the moment the user detaches a zellij
session and disconnects — defeating the whole point of using zellij for
persistent remote work.

Add a user-scope path+service+watcher trio that ties the inhibit lock
to the existence of zellij sessions instead:

  - dot_local/bin/executable_zellij-inhibit-watcher
      Polls `zellij list-sessions --short` every 15s, exits when none
      remain. Override poll interval via $ZELLIJ_INHIBIT_POLL.

  - dot_config/systemd/user/zellij-inhibit-suspend.service
      Wraps the watcher in `systemd-inhibit --what=sleep:idle:handle-lid-switch
      --mode=block`. When the watcher exits, the service stops and the
      lock is released.

  - dot_config/systemd/user/zellij-inhibit-suspend.path
      Activates the service whenever $XDG_RUNTIME_DIR/zellij becomes
      non-empty (i.e. zellij creates its first session socket). Re-fires
      on every empty→non-empty transition.

Enable via systemd-units/user.txt (the .path unit; the service is
on-demand).

The existing SSH-shell inhibitor is kept as a backstop for non-zellij
remote sessions and is now documented as such.

VM (nix/vm.nix) deliberately not updated: the Ubuntu remote-dev VM
never suspends, so the inhibit machinery would be inert there.

0 files changed, 0 insertions, 0 deletions