Normalize probe markers in replay snapshot instruction rows

[espadonne]

Summary

• _snapshot_to_rows calls parse_instruction_body on replay snapshots, but never strips ### Q !probe headers — instruction sections that use probe markers (a documented feature in dlm.eval.probes) round-trip through replay as parse errors and silently drop their training rows
• Wrap the snapshot body in _normalize_probe_markers before parsing, mirroring the pattern already in data.sections_to_rows._section_to_rows and preference.mine._extract_prompts
• Adds a regression test in tests/unit/replay/test_store.py exercising a ### Q !probe snapshot through sample_rows

Test plan

• pytest tests/unit/replay/test_store.py — 14 passed
• mypy --strict src/dlm/replay/ — clean