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/inventories/labelprint/hosts.yml

@@ -0,0 +1,16 @@
+---
+# The 4x6 label print proxy: a Raspberry Pi 3B+ with the Phomemo PM246 on USB,
+# shared to the LAN over IPP/AirPrint. Deliberately a separate inventory from
+# inventories/home: this host is Debian/apt and shares none of the Fedora roles
+# that home.debyl.io runs, so `make deploy` can never reach it by accident.
+#
+# Reached by mDNS (avahi on the Pi, Bonjour/UDM Pro on the LAN) rather than by a
+# DNS record. If the Pi has fallen back to its rescue access point, it is not on
+# the LAN at all -- join the rescue SSID and deploy against 192.168.4.1 instead:
+#
+#   make deploy-labelprint EXTRA_VARS="ansible_host=192.168.4.1"
+labelprint:
+  hosts:
+    stickah.local:
+      ansible_user: stickah
+      ansible_python_interpreter: /usr/bin/python3