Reject control line breaks in test manifests

[codeforester]

Summary

Reject embedded NUL, LF, and CR characters in both test.command and test.mise, matching the validation already applied to other manifest command surfaces.

Issue

Fixes #1890

Validation

• New six-case regression test covering test.command and test.mise with NUL, LF, and CR values
• PYTHONPATH=/Users/rameshhp/work/base-cli/lib/python:cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m unittest cli/python/base_setup/tests/test_manifest.py (52 passed)
• PYTHONPATH=/Users/rameshhp/work/base-cli/lib/python:cli/python /Users/rameshhp/.base.d/base/.venv/bin/pylint --rcfile=.pylintrc cli/python/base_setup/manifest.py cli/python/base_setup/tests/test_manifest.py
• env -u BASE_HOME BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash BASE_CLI_SOURCE_DIR=/Users/rameshhp/work/base-cli/lib/python BASE_CACHE_DIR=/private/tmp/base-v180-small-fixes ./bin/base-test

Demo Impact

None.

Notes

.ai-context/ is unchanged because this is a narrow manifest input-validation hardening, not a product-shape or workflow change.

Checklist

• Branch name follows <category>/<issue>-<YYYYMMDD>-<slug>, and the prefix matches the issue's single standard category label.
• PR is scoped to one issue.
• PR body explains what changed and how it was validated.
• Relevant Python tests and lint pass.
• Bug fix includes regression proof.
• Documentation changes are not needed.
• AI context is not applicable.
• PR includes Fixes #1890.
• Demo impact is explicitly stated.