Add local Docker deployment and submodules

- docker-compose.yml: builder, nginx web server and a LaTeX container (profile "latex")
  for regenerating the SVG drawings
- Makefile, scripts/fetch.sh, .env.example
- 50ohm, 50ohm-contents-dl and 50ohm-ansible as submodules tracking branch sv

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

docker/builder/Dockerfile

@@ -0,0 +1,14 @@
+# Static-site generator for the Swedish 50ohm site.
+# The source is NOT copied into the image: compose bind-mounts ./50ohm at /app
+# so template/renderer edits take effect on the next `make build` without an image rebuild.
+FROM python:3.12-slim
+
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1
+
+WORKDIR /app
+COPY --from=src requirements.txt /tmp/requirements.txt
+RUN pip install --no-cache-dir -r /tmp/requirements.txt
+
+ENTRYPOINT ["python", "main.py"]
+CMD ["-i", "/content", "-o", "/out"]