Guard ColumnRef.sqlName() comparisons against case-sensitivity drift

The column-identity sibling of R358, filed by R358 so the defect does not fall into a blind spot silently. ColumnRef.sqlName() is, like TableRef.tableName(), a case-preserved verbatim identity string, while the jOOQ catalog’s findColumn lookup (JooqCatalog.java:813) is the already-case-insensitive layer (the column analogue of findTable). So the same structural drift exists: one live case-sensitive .sqlName().equals( (GraphitronSchemaValidator.java:883, !rcf.column().sqlName().equals(ocf.column().sqlName())) sits alongside six equalsIgnoreCase comparison sites (FieldBuilder.java, TypeBuilder.java, BuildContext.java, NodeIdLeafResolver.java ×3). R358 scoped itself to tableName and explicitly excluded this; the proportionate fix mirrors R358’s Phase 2: a sameColumn(…​)-style predicate on ColumnRef plus a guard scan, or fold both identity strings into one canonical-identity pass (R358 "Alternatives considered"). Per-site reachability: :883’s operands may, like R358’s `:3105, be non-divergent (it compares two `ColumnRef`s that may share provenance); this item makes that per-site call rather than presuming the defect is live.