Setup Woodpecker CI config

Dockerfile

@@ -1,16 +1,17 @@
-FROM node:16
-
-RUN mkdir /app
-
-COPY package.json /app
-COPY yarn.lock /app
-
-RUN cd /app && yarn install
-
-COPY . /app
-
-RUN rm -rf /app/.env
-RUN touch /app/.env
+FROM node:16-bullseye
 
 WORKDIR /app
+
+# Dependencies first so the install layer caches independently of app source.
+COPY package.json yarn.lock ./
+
+RUN yarn install --frozen-lockfile --network-timeout 600000 \
+ && yarn cache clean
+
+COPY . .
+
+# Config comes from the environment in k8s; libflitter still expects the file
+# to exist, so ship an empty one. (.dockerignore keeps the real .env out.)
+RUN touch /app/.env
+
 CMD ["node", "index.js"]