feat(kernel): preserve union nodes across extraction

codegraph-kernel/src/buffers.rs

@@ -77,7 +77,7 @@ pub const EDGE_ROW_SIZE: usize = 44;
 pub const REF_ROW_SIZE: usize = 40;
 
 /// Mirror of NODE_KINDS in src/types.ts — order is the wire contract.
-pub const NODE_KINDS: [&str; 22] = [
+pub const NODE_KINDS: [&str; 23] = [
     "file",
     "module",
     "class",
@@ -100,6 +100,7 @@ pub const NODE_KINDS: [&str; 22] = [
     "export",
     "route",
     "component",
+    "union",
 ];
 
 /// Mirror of EDGE_KINDS in src/types.ts — order is the wire contract.