check: stamp SK_TYPE value idents with the per-decl NAMED

A TYPE name used as a VALUE (an error-singleton `return too_long;`)
stamped the flattened BODY type, so structurally identical !void
singletons in one union were indistinguishable and flatvariantidxt
loud-rejected the ambiguity — the real cause of the lib/path wwstage
reject (the pinned #120/#29 global-slice-const blame was stale; that
family had drained). The N_IDENT arm resolves through a synthesized
TNAME (the #66 N_STRUCTLIT precedent); the module-qualified N_DOT twin
reads the sym's cached NAMED. Graduates the path M_WWREJECT pin (#142).

test/wcc/data/r142_singleton_value_named/case.ww

@@ -0,0 +1,23 @@
+//ww:run-exit 42
+// #142: a VALUE use of an error-singleton type name whose union has
+// structurally identical siblings. The pre-fix wwstage stamped the
+// flattened BODY type (!void), so flatvariantidxt could not pick a
+// variant and loud-rejected; the per-decl NAMED stamp discriminates.
+// Exit 42 proves the SECOND variant is selected, not the first.
+package main;
+
+type a = !void;
+type b = !void;
+type err = !(a | b);
+
+fn f() err = {
+	return b;
+};
+
+fn main() i32 = {
+	match (f()) {
+	case a => { return 41; };
+	case b => { return 42; };
+	};
+	return 9;
+};