move handleEdgeSelection into store, fix hooks

packages/svelte/src/lib/hooks/useInternalNode.svelte.ts

@@ -0,0 +1,25 @@
+import { useStore } from '$lib/store';
+import type { InternalNode } from '$lib/types';
+
+/**
+ * Hook to get an internal node by id.
+ *
+ * @public
+ * @param id - the node id
+ * @returns a readable with an internal node or undefined
+ */
+export function useInternalNode(id: string): { current: InternalNode | undefined } {
+  const { nodeLookup, nodes } = $derived(useStore());
+
+  const node = $derived.by(() => {
+    // eslint-disable-next-line @typescript-eslint/no-unused-expressions
+    nodes;
+    return nodeLookup.get(id);
+  });
+
+  return {
+    get current() {
+      return node;
+    }
+  };
+}