Add complete HCI protocol module (hci.rs) with packet types, 55+ constants,
command builders (Reset, Read BD Addr, Read Local Version, LE scan/connect),
event parsers, and structured result types. Add USB transport abstraction
(usb_transport.rs) with UsbHciTransport trait and StubTransport for testing.
Wire btusb daemon with endpoint descriptor parsing, HCI init sequence
(Reset → Read BD Addr → Read Local Version), ControllerState state machine,
and enhanced status output. Replace all expect()/unwrap() calls in btctl
and wifictl with proper error handling and graceful fallback.
91 btusb tests, 27 btctl tests, 2 wifictl tests passing.
vasilito