Add buildable, typed PyPI distribution for base_cli

[codeforester]

Goal

Add the first buildable, installable, typed PyPI distribution for base_cli.

Background

The supplied review found no pyproject.toml, setup.cfg, or setup.py; base_cli.__version__ is undefined even though the repository VERSION is 1.7.0; the root license is not packaged; and no py.typed marker or package-level packaging metadata exists. The repository-level pytest.ini also assumes the monorepo layout. These gaps prevent a clean wheel/sdist install and make the package's supported Python contract implicit.

Depends on #1741, the package-name/license decision.

Scope

• Add a standards-based build backend and PEP 621 metadata for the lib/python/base_cli package.
• Expose base_cli.__version__ from the repository version contract and wire the build metadata through a dynamic version declaration.
• Declare the chosen package name, license, supported Python floor, runtime dependencies, optional test dependencies, project URLs, and package README.
• Add and include an empty base_cli/py.typed marker so downstream type checkers consume inline annotations.
• Include the selected license file and other required package data in the sdist and wheel.
• Keep tests out of the runtime wheel unless a deliberate test-distribution policy is documented.

Acceptance Criteria

• python -m build produces a valid sdist and wheel from a clean checkout.
• The built metadata matches the approved name/license decision and declares the actual minimum supported Python version (the code currently requires at least Python 3.9 unless the support policy is intentionally changed).
• A clean virtual environment can install the wheel and run import base_cli; assert base_cli.__version__ == "1.7.0".
• The wheel contains py.typed, the package README, and the selected license metadata/file.
• A minimal documented Click-based command can be imported and run from the installed distribution.
• The package does not depend on the monorepo's cli/python, root pytest.ini, or checkout-only files at runtime.

Validation

• python -m build
• twine check dist/*
• Install the wheel into a fresh virtual environment and run import/version and minimal-command smoke tests.
• Inspect unzip -l dist/*.whl and the sdist file list for package-data and test leakage.
• git diff --check and the focused package tests.

Non-Goals

• Do not publish to PyPI from this issue; publication automation is tracked separately.
• Do not redesign the base_cli API or Base command behavior.
• Do not change the license without resolving the package identity/license decision first.

Project Fields

• Priority: P1
• Size: M
• Area: Packaging
• Initiative: Adoption Polish

Agent Assignment

Human first for the build-backend and metadata contract; implementation can follow the identity/license decision.

[codeforester]

The buildable package contract has moved to https://github.com/basefoundry/base-cli: pyproject.toml, Apache-2.0 metadata, py.typed, package tests, and installable distribution layout are present on main. The guarded sdist/wheel validation and publication workflow is the follow-up in Base #1744 and base-cli PR #2. Closing this packaging-foundation issue as implemented in the standalone repository.