feat: WP-0006 — packaging & distribution infrastructure

CI matrix (Python 3.11/3.12) with pip cache and coverage job. PyPI publish
workflow (OIDC trusted publishing, triggered on v*.*.* tags). Docker image
for REST service with non-root user + ghcr.io push workflow. markidocx
--version flag. Diagram optional extras (diagram-mermaid/graphviz/plantuml)
and readme/urls in pyproject.toml. CHANGELOG.md (Keep a Changelog format)
with retrospective v0.1.0 entry. docs/release-process.md with executable
checklist. All 272 tests pass; ruff and mypy clean; twine check PASSED.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,19 @@
+FROM python:3.12-slim
+
+# Create non-root user
+RUN useradd --create-home --shell /bin/bash appuser
+
+WORKDIR /app
+
+# Install markidocx
+COPY pyproject.toml ./
+COPY src/ ./src/
+RUN pip install --no-cache-dir .
+
+# Switch to non-root user
+USER appuser
+
+EXPOSE 8080
+
+ENTRYPOINT ["markidocx", "serve"]
+CMD ["--host", "0.0.0.0", "--port", "8080"]