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/files/trim-ppd-media.awk

@@ -0,0 +1,25 @@
+# Cuts every media size except one out of a CUPS PPD.
+#
+# macOS and Windows add this printer driverless: they never see this PPD, they
+# see the IPP media-supported list cupsd derives from it. Trimming here is
+# therefore the only way to make 4x6 the single choice a client can offer --
+# there is no lpadmin option that restricts the media list.
+#
+# Regenerated from the driver's own PPD on every deploy, so a driver version
+# bump carries its new PPD through this filter rather than being pinned to a
+# fork.
+#
+#   awk -v keep=w288h432 -f trim-ppd-media.awk tspl-label.ppd
+#
+# The four families below are keyed by the PPD page-size keyword in field 2,
+# which reads as "w288h432/4 x 6 in:" -- hence the split on "/".
+/^\*(PageSize|PageRegion|ImageableArea|PaperDimension) / {
+    split($2, f, "/")
+    if (f[1] != keep) next
+}
+
+# Custom sizes would put "Manage Custom Sizes" back in the client's paper menu
+# and let a job arrive at any dimension, which is the thing being prevented.
+/^\*(CustomPageSize|ParamCustomPageSize|MaxMediaWidth|MaxMediaHeight)/ { next }
+
+{ print }