fix: unify TTY selection logic across ARM64 and AMD64

[Hero2633]

Problem:

On ARM64 servers such as Kunpeng 920, after booting the Harvester ISO, the screen directly shows the rancher login: prompt instead of entering the Harvester interactive installer UI.

Observed behavior:

• The ISO boots successfully
• The system enters the live environment normally
• The local display does not show the Harvester-installer UI
• The screen stays at rancher login:
• harvester-installer output is actually redirected to the serial console (for example ttyS0)

Further investigation showed that this problem is related to the installer's TTY selection logic: when both a local virtual terminal and a serial console are present (for example ttyS0 and tty1), the installer may be bound to the serial console first instead of the local tty1.

Solution:

This PR unifies the TTY selection logic used by the installer so that startup, internal console detection in Go, and getty restart handling all follow the same priority:

tty1 > other virtual ttys > serial console

This PR includes:

• Updating setup-installer.sh to prefer tty1, then other virtual terminals, and fall back to serial console only when no virtual tty is available
• Updating pkg/console/tty.go so the Go-side console selection logic matches the shell-side behavior
• Updating harv-restart-services to use the same priority when restarting the console getty
• Adding / updating tests for TTY selection behavior

This makes console selection behavior consistent across ARM64 and AMD64, and fixes the case where installer output is redirected to serial console even though a local virtual terminal is available.

Related Issue(s):

none

Test plan:

Verified with:

• bash -n package/harvester-os/files/usr/bin/setup-installer.sh
• bash -n package/harvester-os/files/usr/sbin/harv-restart-services
• go test ./pkg/console

Additional documentation or context

In the affected environment, the installer could be manually brought back to the local terminal using:

systemctl stop serial-getty@ttyS0.service
pkill -9 -f harvester-installer
start-installer.sh