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>

src/markidocx/cli.py

@@ -10,6 +10,8 @@ import typer
 from rich.console import Console
 from rich.table import Table
 
+from markidocx import __version__
+
 app = typer.Typer(
     name="markidocx",
     help="Markdown ↔ DOCX round-trip editing system.",
@@ -18,6 +20,22 @@ app = typer.Typer(
 template_app = typer.Typer(help="Template family management.")
 app.add_typer(template_app, name="template")
 
+
+def _version_callback(value: bool) -> None:
+    if value:
+        print(f"markidocx {__version__}")
+        raise typer.Exit()
+
+
+@app.callback()
+def _main(
+    version: Annotated[
+        bool,
+        typer.Option("--version", callback=_version_callback, is_eager=True, help="Show version and exit."),
+    ] = False,
+) -> None:
+    pass
+
 console = Console()
 err_console = Console(stderr=True)