feat(kernel): an edge's meeting sides are sets of origins (merged faces)

EdgeOrigin::Meet now names each side as a Side: the sorted, de-duplicated
origins of the face there. substitute maps a side to the union of the inner
faces' origins, so a meeting with a face an inner operation merged keeps its
lineage; meeting() derives sides from whole faces. Fillets after box cuts
that leave coplanar pieces now report exact history. Prism lineage meets a
cap of several origins and resolves wall junctions away from shared
vertices by the operand's one edge between the walls. bore_union's recut
reports history only for a one-face bore (pieces of a two-arc bore's recut
wall were given both arcs).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J53sR6gEaVt56soFDpTck8

crates/kernel/src/heal.rs

@@ -446,7 +446,7 @@ impl HealMap {
             .map(|(id, under)| {
                 let mut origins = BTreeSet::new();
                 for i in under {
-                    origins.extend(edges.get(*i)?.iter().copied());
+                    origins.extend(edges.get(*i)?.iter().cloned());
                 }
                 Some((*id, origins.into_iter().collect()))
             })