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/ci.yml

@@ -20,6 +20,7 @@ jobs:
         uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
+          cache: "pip"
 
       - name: Install dependencies
         run: pip install -e ".[dev]"
@@ -31,4 +32,30 @@ jobs:
         run: mypy src/
 
       - name: Run tests
-        run: pytest
+        run: pytest --tb=short -q
+
+  coverage:
+    runs-on: ubuntu-latest
+    if: github.ref == 'refs/heads/main'
+    needs: test
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+          cache: "pip"
+
+      - name: Install dependencies
+        run: pip install -e ".[dev]"
+
+      - name: Run tests with coverage
+        run: pytest --cov=markidocx --cov-report=xml --tb=short -q
+
+      - name: Upload coverage report
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-xml
+          path: coverage.xml