fix(cli): lazy-load ScoreVision help paths

[Maa-ly]

Closes #45

Summary

• lazy-load root CLI command groups so root help renders ScoreVision-specific commands without importing every subcommand module
• defer heavy manifest and elements imports until command execution so grouped help paths stay lightweight
• add regression tests covering root help and lazy grouped help from the root CLI

Validation

• uv run sv --help
• uv run sv manifest --help
• uv run sv elements --help
• uv run pytest tests/cli/test_root_help.py tests/cli/test_manifest_create.py tests/cli/test_manifest_validate.py tests/cli/test_manifest_list.py -q

Notes

• this keeps the existing sv entrypoint and command names intact while making help rendering resilient in a fresh source environment