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>

CLAUDE.md

@@ -320,3 +320,5 @@ Then either:
 - MCP tool reference: `~/the-custodian/state-hub/mcp_server/TOOLS.md`
 - ADR-001 (workplan convention): `~/the-custodian/canon/architecture/adr-001-workplans-as-repo-artefacts.md`
 - Contribution convention: `~/the-custodian/canon/standards/contribution-convention_v0.1.md`
+- Release process: `docs/release-process.md`
+- Changelog: `CHANGELOG.md`