Print collection start message

[Tingliangstu]

Summary

• Print an immediate start/progress message before collect begins parsing OUTCAR files through next or the collect command.
• Mark collect steps in smart next so CLI output can identify long collection work before running it.
• Document the collection wait message and test that it appears before final work summary.

Tests

• python -m ruff check src tests
• pytest tests/test_workflow_next.py::test_next_runs_collect_only_config -q
• pytest -q