_fold_confidence normalized the confidence/confidence_score pair on edges
and hyperedges, but nodes passed through the build verbatim, so a model
emitting a lowercase enum value, a bare float, or a drifted word for a
node's confidence landed in graph.json as-is. Fold it in
_fold_node_aliases, which both build_from_json and build_merge already
call, so nodes share one normalization contract with edges.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Covers every shape the issue reports: the non numeric drifted words,
a numeric looking string that still backfills confidence_score, a
case only variant that gets recased rather than treated as an
unknown word, the three valid spellings staying untouched, and the
new hyperedge fold. A build_from_json test reproduces the issue's
own warning text end to end and checks it no longer prints.
(cherry picked from commit da369c5ea8)
