fix: stop getty@tty1 before first-boot setup service to prevent SIGHUP kill

Conflicts=getty@tty1 ensures systemd releases TTY1 before kiosk-setup
runs interactively. Also add partman/choose_partition select finish to
preseed so disk write confirmation is fully automated.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

preseed-bootstrap.sh

@@ -18,6 +18,8 @@ cat > /etc/systemd/system/kiosk-firstboot.service << 'EOF'
 Description=SeniorNet Kiosk First-Boot Setup
 After=network-online.target
 Wants=network-online.target
+Conflicts=getty@tty1.service
+After=getty@tty1.service
 
 [Service]
 Type=oneshot
@@ -26,7 +28,6 @@ StandardInput=tty
 TTYPath=/dev/tty1
 TTYReset=yes
 IgnoreSIGPIPE=no
-SendSIGHUP=yes
 RemainAfterExit=no
 
 [Install]