build: the unix paths retire — configuration, logs, and volumes move into the danos tree

/etc/init.csv and /etc/devices.csv become /system/configuration/*.csv (the
repo's etc/ moves to system/configuration/, mirroring the runtime tree),
/var/log becomes /system/logs, and /mnt/usb becomes /volumes/usb. The
kernel VFS gains a carve-out so FAT may serve exactly /system/configuration
and /system/logs beneath the initrd-backed /system while /system and /test
themselves stay unshadowable; FAT's single /var mount splits into those two
rewritten mounts. The kvfs readdir check learns /system's third child and
the ramdisk spawn sweep skips the configuration tree.

Suite 106/106.

system/drivers/usb-xhci-bus/usb-xhci-bus.zig

@@ -459,7 +459,7 @@ fn reportInterface(manager: ipc.Handle, port: u32, interface: library.InterfaceI
         return null;
     };
     // The devices.csv columns (bus=usb, and the class triple as base/class/prog_if)
-    // then the human-readable interface name — a would-be /etc/devices.csv row read
+    // then the human-readable interface name — a would-be /system/configuration/devices.csv row read
     // straight off the boot log.
     std.log.info("port {d} interface {d}  bus=usb base={X:0>2} class={X:0>2} prog_if={X:0>2}  —  {s}  registered as device {d}", .{
         port,