Fix transcoder Dockerfile to use apt-get for Ubuntu-based image

squashkiwi-streaming/config/transcoder/Dockerfile

@@ -1,7 +1,9 @@
 FROM linuxserver/ffmpeg:latest
 
 # Install fonts for text overlay
-RUN apk add --no-cache ttf-dejavu
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends fonts-dejavu-core && \
+    rm -rf /var/lib/apt/lists/*
 
 # Copy transcoder script
 COPY transcoder.sh /transcoder.sh