Add build infra

Dockerfile.builder

@@ -0,0 +1,18 @@
+# KPN++ Builder Image
+# Pre-built image with GCC, CMake, Ninja, and Python dev headers for building and testing KPN++
+# Build: docker build -f Dockerfile.builder -t gitea.tourolle.paris/dtourolle/kpnpp-builder:latest .
+# Push:  docker push gitea.tourolle.paris/dtourolle/kpnpp-builder:latest
+
+FROM gcc:14
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    cmake \
+    ninja-build \
+    python3 \
+    python3-dev \
+    python3-pip \
+    git \
+    ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /src