Kestrel v0.9.1 beta "More Quality"

Networking works under VirtualBox. The long-standing "arp: timed out
transmitting" was never a transmit bug — an 82540 does not transmit while the
link is down, and never completes the descriptor. QEMU raises link the instant
CTRL.SLU is set; VirtualBox takes over a second, and the boot-time ARP went out
inside that window. The driver now waits for the link.

The desktop is yours. A Settings window with clickable presets, toggles and
steppers, plus every colour and most of the layout changeable from the shell
and kept at /disk/desktop.conf across reboots. Five presets: default, midnight,
paper, amber, matrix.

Windows can be closed from their title bar and reopened from the launcher, the
desktop shortcuts, or `open <window>`.

Also: a `nic` command that dumps the network card's own registers, and `version`
reporting what this build is.

Known limitations are listed in the README. The notable ones are no TLS, no
window resizing, and one window of each kind.