feat: streamline chains runtime and overview

[TacoRocket]

Summary

• decouple live chains families from emitted source-command artifact reloads
• add chains overview/help parity and CSV coverage for the browse surface
• extend visibility-tier coverage for env-vars and chains while tightening chain runtime cleanup

Validation

• python3 -m ruff check src tests scripts
• PYTHONPATH=src python3 scripts/generate_schemas.py
• PYTHONPATH=src python3 -m pytest tests/test_collectors.py tests/test_golden_outputs.py tests/test_contract_schemas.py tests/test_cli_smoke.py tests/test_help.py tests/test_terminal_ux.py tests/test_models.py
• pre-push guardrail: 300 passed, 2 deselected
• cleanup-pass review
• ai-smell-review
• post-slice-plan-review