feat: add MongoDB support with connection pooling and repository pattern

Dockerfile

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+# Use the official Rust image as a base
+FROM rust:bookworm as builder
+
+# Set the working directory
+WORKDIR /app
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y \
+    pkg-config \
+    libssl-dev \
+    # Add any other dependencies required by your project
+    # For example, if you use postgres/mysql/sqlite, you might need libpq-dev, libmysqlclient-dev, libsqlite3-dev
+    && rm -rf /var/lib/apt/lists/*
+
+# Copy the Cargo.toml and Cargo.lock first to leverage Docker cache
+# This layer only rebuilds if dependencies change
+COPY Cargo.toml Cargo.lock ./
+
+# Create a dummy src directory and main.rs to build dependencies
+# This caches the dependency build
+RUN mkdir -p src && echo "fn main() {println!(\"hello world\");}" > src/main.rs
+# Build dependencies
+RUN cargo build --release && rm -rf src
+
+# Copy the actual source code
+COPY . .
+
+# Build the release binary
+RUN cargo build --release
+
+# --- Start a new stage for a smaller final image ---
+FROM debian:bookworm-slim
+
+# Set the working directory
+WORKDIR /app
+
+# Install runtime dependencies if any
+# For example, if your Rust application dynamically links to OpenSSL, you might need libssl3
+RUN apt-get update && apt-get install -y \
+    libssl3 \
+    # Add any other runtime dependencies here
+    && rm -rf /var/lib/apt/lists/*
+
+# Copy the built binary from the builder stage
+COPY --from=builder /app/target/release/employee-tracking-backend .
+
+# Expose the port your application listens on
+EXPOSE 3000
+
+# Set the entrypoint command to run your application
+CMD ["./employee-tracking-backend"]