Soften pre-Agon agent service boundary

[8Dionysus]

Summary

• reframe AGENT_SUBJECT_PREP as a holding boundary rather than a planted seed pack
• name the civil/service assistant path and future additive adjunct families
• keep schemas, generated surfaces, and core profile shape unchanged

Tests

• python -m pytest -q tests/test_roadmap_parity.py
• python scripts/validate_agents.py
• python -m pytest -q tests
• git diff --check