After upgrading a serial-console 1.4.x installation to rolling with `add system image`, the system boots on serial once. Then the GRUB console order flips and boot output goes to the KVM/VGA console instead of the serial port. The `31-to-32` migration does not add `system console device ttyS0 kernel`, although the system booted on ttyS0.
## Steps to reproduce
- Have 1.4.5 installed alongside a legacy 1.3.x image, booting on serial (`console=tty0 console=ttyS0,115200`), with `system console device ttyS0 speed 115200`
- Run: `add system image <rolling ISO>`
- Reboot (boot 1): still on serial, but the migrated config lacks `system console device ttyS0 kernel`
- Reboot (boot 2): cmdline is now `console=ttyS0,115200 console=tty0`, so there is no boot output on serial.
## Root cause
The installed legacy 1.3.x image keeps GRUB in compat mode (`VYOS_CFG_VER=0`), so vyos-grub-update.service rewrites the GRUB vars on every boot, before migration runs. `31-to-32` reads `console_type` from those vars instead of the console the system booted on,
and skips. Without `kernel` in the config, the console conf-mode script then writes `console_type=tty` to the GRUB vars, which flips the console order on the next boot.
## Proposed Fix
Treat the kernel's boot console as authoritative. `31-to-32` takes the last `console=` argument on `/proc/cmdline`. If it is the flavor's serial device and that device is configured, it sets `kernel`. If it is `tty0`, it changes nothing. GRUB vars are only a fallback when the Kernel cmdline has no `console=`.