Pretty-print workspace JSON output

[codeforester]

Summary

• Pretty-print basectl workspace status|check|doctor --format json output.
• Add regression assertions that workspace JSON is multi-line and still parseable.
• Note the workspace JSON readability fix in the changelog.

Validation

• env -u BASE_HOME PYTHONPATH=/Users/rameshhp/work/base-worktrees/fix-550-pretty-workspace-json/lib/python:/Users/rameshhp/work/base-worktrees/fix-550-pretty-workspace-json/cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pytest cli/python/base_projects/tests/test_engine.py cli/python/base_projects/tests/test_workspace_checks.py cli/python/base_projects/tests/test_workspace_status_manifest.py -q
• ./bin/basectl workspace status --workspace /Users/rameshhp/work --manifest /Users/rameshhp/work/base-workspace.yaml --format json
• env -u BASE_HOME PYTHONPATH=/Users/rameshhp/work/base-worktrees/fix-550-pretty-workspace-json/lib/python:/Users/rameshhp/work/base-worktrees/fix-550-pretty-workspace-json/cli/python /Users/rameshhp/.base.d/base/.venv/bin/python -m pylint --rcfile=.pylintrc cli/python/base_projects/engine.py cli/python/base_projects/workspace_reports.py cli/python/base_projects/tests/test_engine.py cli/python/base_projects/tests/test_workspace_checks.py cli/python/base_projects/tests/test_workspace_status_manifest.py
• git diff --check
• git diff --cached --check
• env -u BASE_HOME ./bin/base-test

Demo Impact

• Workspace JSON output is easier to inspect in terminal demos. Payload schema is unchanged.

Fixes #550