[codex] Borrow factlog source support signals

[justinjoy]

Summary

• add deterministic source corroboration helpers for engine-input facts
• parse functional relation declarations and report single-valued competing values with per-value source support
• show the source support and single-valued conflict views on the dashboard

Notes

• This intentionally does not auto-accept candidate facts. It only ports factlog features that already exist there: source support counts and deterministic single-valued conflict views.
• LLM confidence is not used by these signals.

Validation

• .venv/bin/python -m pytest -q