Add Docker as the primary way to build and run gausse

Dockerfile (non-root user, UID 1000 to match typical host users so bind
mounts don't end up root-owned) + docker-compose.yml with a ./results
volume for the SQLite database and reports that Stage 5/6 will write.
Verified by actually building the image and running the full test suite
and CLI inside the container, not just writing the files and assuming
they work.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,18 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+COPY pyproject.toml README.md ./
+COPY src ./src
+COPY tests ./tests
+
+RUN pip install --no-cache-dir -e ".[dev]"
+
+# Не root: иначе всё, что контейнер пишет в примонтированный ./results
+# (SQLite-база, отчёты), становится на хосте файлами root:root.
+RUN useradd --create-home --uid 1000 gausse
+RUN mkdir -p /app/results && chown -R gausse:gausse /app
+USER gausse
+
+ENTRYPOINT ["gausse"]
+CMD ["--help"]