Add Dockerfile

I added this so that I could run a nak bunker on my server alongside my other containers. Thought it might be useful for others.

Dockerfile

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+# build stage
+FROM golang:1.24-alpine AS builder
+
+# install git and ca-certificates (needed for fetching dependencies)
+RUN apk add --no-cache git ca-certificates
+
+# set working directory
+WORKDIR /app
+
+# copy go mod files first for better caching
+COPY go.mod go.sum ./
+
+# download dependencies
+RUN go mod download
+
+# copy source code
+COPY . .
+
+# build the application
+# use cgo_enabled=0 to create a static binary
+# use -ldflags to strip debug info and reduce binary size
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o nak .
+
+# runtime stage
+FROM alpine:latest
+
+# install ca-certificates for https requests (needed for relay connections)
+RUN apk --no-cache add ca-certificates
+
+# create a non-root user
+RUN adduser -D -s /bin/sh nakuser
+
+# set working directory
+WORKDIR /home/nakuser
+
+# copy the binary from builder stage
+COPY --from=builder /app/nak /usr/local/bin/nak
+
+# make sure the binary is executable
+RUN chmod +x /usr/local/bin/nak
+
+# switch to non-root user
+USER nakuser
+
+# set the entrypoint
+ENTRYPOINT ["nak"]
+
+# default command (show help)
+CMD ["--help"]