Install a font in the image

python:3.12-slim ships no font files, so Pillow fell back to its 10-pixel
bitmap font and every printed label came out with sub-millimetre text.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vunz4VLxAYDBnU5tLciLDC

Dockerfile

@@ -13,11 +13,17 @@ ENV PYTHONUNBUFFERED=1 \
 
 # libpq for psycopg, and the runtime libs PyMuPDF/Pillow need for
 # PDF thumbnails and image handling.
+#
+# fonts-dejavu-core is not optional: python:3.12-slim ships no font files,
+# and without one Pillow silently falls back to a 10-pixel bitmap font.
+# Part labels then print letters under a millimetre tall - legible on
+# screen, unreadable on the sticker.
 RUN apt-get update && apt-get install -y --no-install-recommends \
         libpq5 \
         libjpeg62-turbo \
         zlib1g \
         libfreetype6 \
+        fonts-dejavu-core \
         curl \
     && rm -rf /var/lib/apt/lists/*