feat(labelprint): 4x6 label print proxy on a Raspberry Pi

A Pi 3B+ (stickah.local) shares a Phomemo PM246 to the LAN as a plain CUPS
queue, so any machine can print 4x6 labels -- fulfillr-site's shipping labels
in particular -- without installing the vendor driver, which is x86-64 only.
The role builds the TSPL CUPS driver from source instead.

It is Debian, not Fedora, so it lives in its own inventory and playbook
(make deploy-labelprint / check-labelprint) and the home.debyl.io roles can
never run against it. make bootfs renders its cloud-init first-boot files onto
a freshly imaged SD card from the same templates the role uses. The Wi-Fi
credentials for the home and rescue networks are in the vault.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ansible/roles/labelprint/templates/wifi-rescue.timer.j2

@@ -0,0 +1,13 @@
+# {{ ansible_managed }}
+[Unit]
+Description=Run the Wi-Fi rescue watchdog every {{ labelprint_watchdog_interval_secs }}s
+
+[Timer]
+# Waits for NetworkManager to have had a fair go at the home SSID before the
+# first check, so a slow DHCP lease at boot does not trip the rescue AP.
+OnBootSec=90
+OnUnitActiveSec={{ labelprint_watchdog_interval_secs }}
+AccuracySec=5
+
+[Install]
+WantedBy=timers.target