Restore production Dockerfile (deleted by upstream merge)

Dockerfile

@@ -0,0 +1,37 @@
+# Simple production Dockerfile for tuwunel
+# Built by buildkitd on the x86_64 server — no cross-compilation needed.
+
+FROM rust:slim-bookworm AS builder
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    libclang-dev clang cmake pkg-config make liburing-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /usr/src/tuwunel
+
+# Copy manifests first for dependency caching
+COPY Cargo.toml Cargo.lock rust-toolchain.toml ./
+COPY .cargo/ .cargo/
+COPY src/ src/
+
+# Strip unnecessary cross-compilation targets from rust-toolchain.toml
+# to avoid downloading toolchains we don't need
+RUN sed -i '/x86_64-unknown-linux-musl/d; /aarch64-/d; /apple-/d; /rust-src/d; /rust-analyzer/d; /rustfmt/d; /clippy/d' rust-toolchain.toml
+
+RUN --mount=type=cache,target=/usr/local/cargo/registry \
+    --mount=type=cache,target=/usr/local/cargo/git \
+    cargo build --release --locked \
+    && cp target/release/tuwunel /usr/local/bin/tuwunel
+
+FROM debian:bookworm-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ca-certificates tini liburing2 \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /usr/local/bin/tuwunel /usr/local/bin/tuwunel
+
+EXPOSE 6167
+
+ENTRYPOINT ["tini", "--"]
+CMD ["tuwunel"]