Get Conversation System Prompt

Return the system prompt that would be sent on the next turn.

Reconstructed live from current user state (profile, soul, memory, onboarding status, tool availability) so the UI doesn't show a stale snapshot from the first turn of the session.

Known approximations:

• The preview omits specialist tool guidelines that get appended mid-turn when the LLM calls list_capabilities to activate a category. It matches the start-of-turn tool list, mirroring how the agent itself starts each turn fresh.
• Tools whose factories require a storage backend or an outbound publish hook (currently send_media_reply, upload_to_storage, and move_file) are filtered out by the registry's dependency gates because the preview can't safely construct those runtime hooks. Their usage hints will not appear in the Tool Guidelines section.
• If a user's BOOTSTRAP.md cannot be created on disk by the runtime (rare, requires an OS-level error), the runtime drops out of onboarding mode while this preview still reports is_onboarding=true based on the in-memory heuristic.