dockerfile: fix freebind building, set up everything in one step

this also shrinks the image by around 40MB, since the apt/lists layer no longer sticks around

Dockerfile

@@ -1,14 +1,13 @@
 FROM node:18-bullseye-slim
 WORKDIR /app
 
-RUN apt-get update
-RUN apt-get install -y git
-RUN rm -rf /var/lib/apt/lists/*
-
 COPY package*.json ./
-RUN npm install
 
-RUN git clone -n https://github.com/imputnet/cobalt.git --depth 1 && mv cobalt/.git ./ && rm -rf cobalt
+RUN apt-get update && \
+    apt-get install -y git python3 build-essential && \
+    npm install && \
+    apt purge --autoremove -y python3 build-essential && \
+    rm -rf ~/.cache/ /var/lib/apt/lists/*
 
 COPY . .
 EXPOSE 9000