When MCP elicitation is unavailable (most clients), fall back to
org.freedesktop.Notifications with Approve/Deny action buttons.
Opt-in via MCDBUS_NOTIFY_CONFIRM=1. Silence (timeout) is denial.
Fixes signal race where NotificationClosed stomped ActionInvoked
result in the same event loop iteration.
Bridge Linux D-Bus IPC into MCP with tools for service discovery
(list_services, introspect, list_objects), method calls and property
access, plus convenience shortcuts for notifications, systemd units,
and MPRIS media player control. All 25 tests passing.
