feat(pdftract-68pe): add Dockerfile with FEATURES build-arg support

Adds multi-stage Dockerfile supporting three feature variants:
- default: baseline features, distroless base (~20 MB)
- ocr: default + OCR (Tesseract), debian-slim base (~120 MB)
- full: all features, debian-slim base (~140 MB)

The FEATURES build-arg selects the variant at build time.

Bead: pdftract-68pe
Plan: Release Engineering / Argo WorkflowTemplates, line 3392

Dockerfile

@@ -0,0 +1,65 @@
+# Dockerfile for pdftract
+# Build arg FEATURES selects the feature set: default | ocr | full
+# - default: baseline features, distroless base (~20 MB)
+# - ocr: default + OCR (Tesseract), debian-slim base (~120 MB)
+# - full: all features, debian-slim base (~140 MB)
+
+ARG FEATURES=default
+
+# Build stage: use Debian slim for Rust toolchain
+FROM debian:bookworm-slim AS builder
+
+ARG FEATURES
+# Install build dependencies
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ca-certificates \
+    curl \
+    pkg-config \
+    libssl-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install Rust via rustup
+ENV RUSTUP_HOME=/usr/local/rustup \
+    CARGO_HOME=/usr/local/cargo \
+    PATH=/usr/local/cargo/bin:$PATH
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --profile minimal && \
+    rustup target add x86_64-unknown-linux-gnu
+
+WORKDIR /usr/src/pdftract
+
+# Copy source
+COPY Cargo.toml Cargo.lock ./
+COPY crates/ ./crates/
+
+# Build with requested features
+RUN cargo build --release --features ${FEATURES}
+
+# Runtime stage: conditional base based on FEATURES
+FROM gcr.io/distroless/cc-debian12 AS runtime-default
+FROM debian:bookworm-slim AS runtime-ocr
+FROM debian:bookworm-slim AS runtime-full
+
+# Select runtime stage based on FEATURES
+FROM runtime-${FEATURES}
+
+# Install Tesseract for ocr/full variants
+ARG FEATURES
+RUN if [ "${FEATURES}" != "default" ]; then \
+    apt-get update && \
+    apt-get install -y --no-install-recommends \
+    tesseract-ocr \
+    tesseract-ocr-eng \
+    libliblept5 \
+    && rm -rf /var/lib/apt/lists/*; \
+    fi
+
+# Copy binary from builder
+COPY --from=builder /usr/local/cargo/bin/pdftract /usr/local/bin/pdftract
+
+# Copy license files to /usr/share/doc/pdftract/
+RUN mkdir -p /usr/share/doc/pdftract
+COPY LICENSE-MIT LICENSE-APACHE /usr/share/doc/pdftract/
+
+# Set entrypoint
+ENTRYPOINT ["/usr/local/bin/pdftract"]
+CMD ["--help"]