feat: add docker ci

Dockerfile

@@ -0,0 +1,39 @@
+# ── Build Stage ──────────────────────────────────────────────────────────────
+FROM rust:1.86.0-slim AS builder
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y \
+    pkg-config \
+    libssl-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+# Cache dependencies
+COPY Cargo.toml Cargo.lock rust-toolchain.toml ./
+
+RUN mkdir src && echo "fn main() {}" > src/main.rs
+RUN cargo build --release
+RUN rm -rf src
+
+# Build actual app
+COPY src ./src
+RUN cargo build --release
+
+# ── Runtime Stage ─────────────────────────────────────────────────────────────
+FROM debian:bookworm-slim
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y \
+    ca-certificates \
+    libssl3 \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN useradd -m appuser
+USER appuser
+
+COPY --from=builder /app/target/release/chat .
+
+EXPOSE 3000
+
+CMD ["./chat"]