feat: wait up to 10s for a late MONTAUKROOT, retry USB enumeration after a port reset, recover halted EP0/bulk endpoints, MSC card reader settle

docs/raspberry-pi.md

@@ -25,6 +25,11 @@ module. Finding no ramdisk, the kernel mounts the partition labelled
 `MONTAUKROOT` as `0:/` (`Fs/Boot.cpp`), read through the SD driver
 (`Drivers/Storage/Sdhci`), and the ESP after it. Files load as they are
 used instead of the firmware reading the whole 80 MB tree before boot.
+The card can also boot from a USB card reader (or the image from a USB
+stick): the root then comes through `Drivers/USB/MassStorage.cpp`. A USB
+root can register after the boot scan (a SuperSpeed link still training, a
+reader still bringing its card up), so a boot that finds no `MONTAUKROOT`
+waits up to 10 s for one, servicing USB hot-plug meanwhile.
 Unlike the ramdisk, the root is persistent: changes to `0:/` survive a
 reboot, so shut down from the desktop rather than pulling power.
 The image is sized to its contents (`ROOT_FREE_MIB`, default 64, sets the