Suppress pip version notices in setup

[codeforester]

Summary

• Add --disable-pip-version-check to Base-owned pip installs in the shell bootstrap path.
• Route Python artifact pip installs through one command builder with the same flag for dry-run, batch, and sequential retry paths.
• Add BATS/Python coverage and a changelog note for the setup-output behavior.

Issue

Fixes #911

Validation

• RED: BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats -f "setup installs Base Python packages without pip self-version notices" cli/bash/commands/basectl/tests/setup.bats failed before implementation because the flag was missing.
• RED: PYTHONPATH=lib/python:cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pytest cli/python/base_setup/tests/test_artifacts.py -k "python_artifact_honors_project_venv_dir_override or reconcile_artifacts_batches_python_installs or retries_python_installs" -q failed before implementation because the generated pip commands lacked the flag.
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats -f "setup installs Base Python packages without pip self-version notices" cli/bash/commands/basectl/tests/setup.bats
• PYTHONPATH=lib/python:cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pytest cli/python/base_setup/tests/test_artifacts.py -k "python_artifact_honors_project_venv_dir_override or reconcile_artifacts_batches_python_installs or retries_python_installs" -q
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats cli/bash/commands/basectl/tests/setup.bats
• PYTHONPATH=lib/python:cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pytest cli/python/base_setup/tests/test_artifacts.py -q
• git diff --check
• env -u BASE_HOME BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash ./bin/base-test

Demo Impact

None. Setup-output polish only.

Notes

Base does not auto-upgrade pip; it only suppresses pip self-version notices for Base-owned installs.