chore: add changelog and documentation updates

- Created a new `CHANGELOG.md` file to document all notable changes to the project, adhering to the Keep a Changelog format.
- Updated `CONTRIBUTING.md` to include instructions for building and previewing documentation using MkDocs.
- Added `mkdocs.yml` configuration for documentation generation, including navigation structure and theme settings.
- Enhanced various documentation files, including API reference, architecture overview, configuration reference, and runbook, to provide comprehensive guidance for users and developers.
- Included new sections in the README for changelog and documentation links, improving accessibility to project information.

duty_teller/db/__init__.py

@@ -49,6 +49,12 @@ __all__ = [
 
 
 def init_db(database_url: str) -> None:
-    """Create tables from metadata (Alembic migrations handle schema in production)."""
+    """Create all tables from SQLAlchemy metadata.
+
+    Prefer Alembic migrations for schema changes in production.
+
+    Args:
+        database_url: SQLAlchemy database URL.
+    """
     engine = get_engine(database_url)
     Base.metadata.create_all(bind=engine)