feat(build): add Docker support for emailks service

- Create multi-stage Dockerfile with builder and runtime stages
- Add .dockerignore to exclude unnecessary files and directories
- Configure builder stage with Rust toolchain and dependencies
- Set up runtime stage with minimal Debian base image
- Copy compiled binary from builder to runtime stage
- Expose port 50051 for gRPC service
- Add proper dependency caching for faster builds
- Include SSL certificates and required libraries in runtime

.dockerignore

@@ -0,0 +1,4 @@
+target/
+.git/
+.idea/
+**/*.md

Dockerfile

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+# ---- builder ----
+FROM rust:1.96-slim-bookworm AS builder
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    pkg-config \
+    libssl-dev \
+    protobuf-compiler \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+# Cache dependencies
+COPY Cargo.toml Cargo.lock ./
+COPY build.rs ./
+COPY proto/ proto/
+RUN echo '' >lib.rs && \
+    echo 'fn main() {}' >main.rs && \
+    cargo build --release; \
+    rm -f lib.rs main.rs
+
+# Build real binary
+COPY . .
+RUN cargo build --release --bin emailks && \
+    cp target/release/emailks /app/emailks
+
+# ---- runtime ----
+FROM debian:bookworm-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ca-certificates \
+    libssl3 \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /app/emailks /usr/local/bin/emailks
+
+EXPOSE 50051
+
+ENTRYPOINT ["emailks"]