⚡️(backend) clean package manager cache in Docker builds

Remove package manager index caches in Dockerfile to reduce image size and
improve deployment speed.

Even in multi-stage builds, ensure no unnecessary cache data is stored.
Package indexes are redundant for runtime operation and only increase storage,
bandwidth, and deployment time.

Dockerfile

@@ -62,7 +62,7 @@ FROM base AS core
 
 ENV PYTHONUNBUFFERED=1
 
-RUN apk add \
+RUN apk --no-cache add \
   cairo \
   gdk-pixbuf \
   gettext \