versapad.json declared samd21g18a (256K flash / 32K RAM) while the
linker script, the NVM config addresses (0x1FB00-0x1FFFF, just below
the 128K boundary) and versapad_nobl.json all point to the actual
chip, a SAMD21G17D (128K flash / 16K RAM). PlatformIO's flash-size
check was silently using a ~248K limit instead of the real ~120K
budget for the USB-bootloader build variant.
