Make documented Python test commands use the same base-cli source as CI #1914

Goal

Make the documented local Python test and lint commands reproduce the dependency topology used by CI and bin/base-test.

Evidence

• docs/testing.md:65-69 instructs users to run PYTHONPATH=cli/python python -m pytest.
• Base production code imports APIs from the standalone base-cli package, including ConfigurationError.
• requirements-dev.txt installs the published base-cli==0.4.2, but the installed package in the current Base environment does not expose that source-level API.
• Running PYTHONPATH=cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pytest cli/python/base_setup/tests/test_remote_installers.py -q fails during collection with ImportError: cannot import name 'ConfigurationError' from 'base_cli'.
• .github/workflows/tests.yml succeeds by prepending .dependencies/base-cli/lib/python:lib/python:cli/python, and bin/base-test resolves the sibling checkout or BASE_CLI_SOURCE_DIR.

Scope

• Choose one canonical local command for the Python suite and coverage run.
• Update docs/testing.md, contributor guidance, and any lint instructions to include the required base-cli source path or route through bin/base-test.
• Keep the supported packaged-install path explicit if the published package is intentionally not source-compatible.
• Add a documentation/contract test or smoke check that catches a missing base-cli source path when the docs are changed.

Acceptance criteria

• A new contributor following the documented command reaches test collection without a base_cli import mismatch.
• Local commands and CI use the same explicit source/dependency contract.
• The full bin/base-test path remains green.
• Documentation explains the standard sibling checkout and the BASE_CLI_SOURCE_DIR override.

Project Fields

• Status: Ready
• Priority: P2
• Size: S
• Area: CI
• Initiative: Contract Hardening