feat: implement selection

frontend/src/lib/components/graph/stores.ts

@@ -0,0 +1,10 @@
+import type { Node, Socket } from "$lib/types";
+import { writable, type Writable } from "svelte/store";
+
+export const activeNodeId: Writable<number> = writable(-1);
+export const selectedNodes: Writable<Set<number> | null> = writable(null);
+
+export const activeSocket: Writable<Socket | null> = writable(null);
+export const hoveredSocket: Writable<Socket | null> = writable(null);
+export const possibleSockets: Writable<Socket[]> = writable([]);
+export const possibleSocketIds: Writable<Set<string> | null> = writable(null);