Three-pillar fix from Hamilton review:
Code quality — validate_signature() for D-Bus spec compliance,
MCDBUS_TIMEOUT env var, replace 13 error-as-success returns with
ToolError, monotonic clock deadline on tree walks, sanitize D-Bus
error messages, fix resource connection leak via module-level
BusManager, hasattr guards in conftest.
Elicitation — ctx.elicit() confirmation for system bus call_method
and all set_property calls, graceful degradation when client lacks
elicitation support, MCDBUS_REQUIRE_ELICITATION for hard-fail mode.
Permission docs — four-layer guide (systemd sandboxing, dbus-broker
policy, polkit rules, xdg-dbus-proxy) with ready-to-deploy example
configs validated against xmllint, bash -n, and systemd-analyze.
Fix get_mgr() to use ctx.lifespan_context (works in both request
and standalone Client mode). Add autouse fixture to reset
event-loop-bound singleton state per test, preventing cross-test
asyncio.Event contamination.
21 new tests exercise all 14 tools through FastMCP's in-memory
transport. New shortcuts: network_status (NetworkManager),
battery_status (UPower), bluetooth_devices (bluez),
kwin_windows (KRunner WindowsRunner). 53 tests pass.
