daemon: forward GUI envs; use user XDG config;

[jamesmcm]

• Forward essential X/Wayland env vars from client to daemon-launched apps: DISPLAY, WAYLAND_DISPLAY, XAUTHORITY, XDG_RUNTIME_DIR, XDG_CONFIG_HOME, XDG_SESSION_TYPE, MOZ_ENABLE_WAYLAND, QT_QPA_PLATFORM, GTK_MODULES, GTK3_MODULES, I3SOCK. Default XDG_RUNTIME_DIR to /run/user/ when missing.
• Extend DaemonRequest to carry the forwarded env map; merge into child env in daemon path.
• Respect XDG_CONFIG_HOME in daemon mode: add thread-local config_dir override and set it per client to forwarded XDG_CONFIG_HOME (if it exists) or fall back to ~/.config of the connecting user. Clear the override when the handler exits. This fixes false “config files … do not exist” when the daemon runs under systemd.
• Demote noisy “Could not get PULSE_SERVER from host” to debug in daemon mode (still warn in non-daemon). Daemon continues to set PULSE_SERVER to unix:/run/user//pulse/native for the connecting user.
• Add daemon mode flag in core (set_daemon_mode/is_daemon_mode); mark daemon context in main and use it for conditional logging.
• Avoid interactive auto-sync in daemon mode: setup_namespace now accepts auto_sync_if_missing; daemon passes false (bails with a clear message if configs are missing), CLI path passes true (preserving previous behavior).
• Pass env and stdio consistently for both TTY and non-TTY client cases.

Result:

• GUI apps launched via the daemon get correct X/Wayland/desktop env and no longer fail with “no DISPLAY”.
• Daemon resolves configs from the user’s XDG config dir instead of /root/.config under systemd.
• Systemd logs are quieter; no spurious PULSE warnings or “not a terminal” from attempted interactive sync.