🐛 fix: Dockerfile.prod.template to build binary during Docker build

docker/Dockerfile.prod.template

@@ -2,9 +2,13 @@
 # Minimal image using pre-built binary from CI cache
 # Template: Replace {{DEPS_HASH}} with actual dependency hash
 
-# Use the build cache image as base
+# Use the build cache image as base for building
 FROM gitea.arcodange.lab/arcodange/dance-lessons-coach-build-cache:{{DEPS_HASH}} AS builder
 
+# Set working directory and build the binary
+WORKDIR /workspace
+RUN go build -o dance-lessons-coach ./cmd/server
+
 # Final minimal image
 FROM alpine:3.18