1.1: Launch apps through the systemd user session; console as the launch user

Match the anland-session architecture (~/anland a076ee1): anland-session
publishes the app environment in ~/.anlandx-env and as the systemd user
session environment.

- launchApp: desktop-user launches go through systemd-run --user
  (transient app.slice unit, session env inherited, env prefix
  re-asserts probed/custom values) — no detached fallback, a down user
  manager fails the launch loudly; root launches keep the direct path
- session probe reads ~/.anlandx-env (E_ lines) and overlays the
  built-in env: XDG_RUNTIME_DIR=/run/user/<uid>,
  WAYLAND_DISPLAY=wayland-anland, DBUS, PULSE_SERVER when the session
  runs; ~/.anlandx still supplies DISPLAY (:N from anlandx Xwayland)
- env merge order: built-ins < session env < user custom < probed
  bus/display/xauth
- console: runs as the selected launch user (auto = first non-root
  account of listUsers, reusing the user list), title shows the user;
  preamble sources ~/.anlandx-env and exports DISPLAY
- anlandxInstalled: per launch user, checks anland-session (new) or
  anlandx-start (old); Apps tab shows "Apps - Anlandx not installed"
  when missing for the selected user

Co-authored-by: glm-5.3 <noreply@z.ai>