test: cover calendar subscriptions end to end in Docker

Dockerfile

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+# syntax=docker/dockerfile:1
+FROM rust:1.98.1-bookworm AS build
+WORKDIR /build
+COPY Cargo.toml Cargo.lock rust-toolchain.toml ./
+COPY src ./src
+RUN --mount=type=cache,target=/usr/local/cargo/registry \
+    --mount=type=cache,target=/build/target \
+    cargo build --release --locked && \
+    cp target/release/vacationplanner2ics /usr/local/bin/vacationplanner2ics
+
+FROM python:3.14-slim-bookworm AS test
+RUN pip install --no-cache-dir icalendar==7.3.0
+COPY --from=build /usr/local/bin/vacationplanner2ics /usr/local/bin/
+COPY tests /tests
+ENV PYTHONDONTWRITEBYTECODE=1
+USER 65532:65532
+CMD ["python", "/tests/e2e.py"]
+
+FROM debian:bookworm-slim AS runtime
+RUN apt-get update && apt-get install -y --no-install-recommends ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+COPY --from=build /usr/local/bin/vacationplanner2ics /usr/local/bin/
+USER 65532:65532
+EXPOSE 8080
+ENTRYPOINT ["vacationplanner2ics"]