perf(javascript): reuse graph buckets and query indexes

Append overlapping observations to node buckets instead of recopying groups, and share one node index across semantic seed admission and traversal. Preserve merged provenance and absent-seed behavior.

src/domain/javascript/javascriptRuntimeReconciliationGraph.ts

@@ -212,8 +212,11 @@ const graphCoverage = (
 
 const mergeNodes = (nodes: readonly ApplicationNode[]): ApplicationNode[] => {
   const grouped = new Map<string, ApplicationNode[]>();
-  for (const node of nodes)
-    grouped.set(node.node_id, [...(grouped.get(node.node_id) ?? []), node]);
+  for (const node of nodes) {
+    const group = grouped.get(node.node_id);
+    if (group === undefined) grouped.set(node.node_id, [node]);
+    else group.push(node);
+  }
   const merged = [...grouped.values()].map((group) => {
     const first = group[0];
     if (first === undefined) throw new TypeError("Empty JAG node group");