get_causal_chain() matched only the canonical uppercase spellings
(CAUSED, INFLUENCED, PRECEDENT_FOR), while CausalChainAnalyzer's
vocabulary includes the present-tense forms (causes, influences,
leads_to, supports) — and the two differ in word form, not just case,
so case-insensitive matching alone would still miss them. An edge
recorded as "causes" produced an empty audit chain.
Storage normalizes both vocabularies onto the canonical types via
_CAUSAL_EDGE_ALIASES; traversal accepts the union (_CAUSAL_TRAVERSAL_TYPES).
add_causal_relationship() now accepts either spelling and stores the
canonical form.