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>

.github/workflows/publish.yml

@@ -0,0 +1,33 @@
+name: Publish to PyPI
+
+on:
+  push:
+    tags:
+      - "v*.*.*"
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    permissions:
+      id-token: write  # required for OIDC trusted publishing
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+          cache: "pip"
+
+      - name: Install build tools
+        run: pip install build twine
+
+      - name: Build distribution
+        run: python -m build
+
+      - name: Check distribution
+        run: twine check dist/*
+
+      - name: Publish to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1