feat(FN-2855): route scheduled tasks using effective node resolution

- Add an effective node resolver with task override, project default, and local fallback precedence.
- Wire scheduler dispatch to persist effectiveNodeId/effectiveNodeSource and log resolved node routing.
- Add coverage for effective node resolution and scheduler node routing integration behavior.
- Stabilize workspace test resolution by adding @fusion/core and @fusion/plugin-sdk aliases across Vitest configs.

packages/engine/src/effective-node.ts

@@ -0,0 +1,27 @@
+import type { ProjectSettings, Task } from "@fusion/core";
+
+export type EffectiveNodeSource = "task-override" | "project-default" | "local";
+
+export interface EffectiveNode {
+  nodeId: string | undefined;
+  source: EffectiveNodeSource;
+}
+
+function isSetNodeId(nodeId: string | null | undefined): nodeId is string {
+  return typeof nodeId === "string" && nodeId.trim().length > 0;
+}
+
+export function resolveEffectiveNode(
+  task: Pick<Task, "nodeId">,
+  settings: Pick<ProjectSettings, "defaultNodeId">,
+): EffectiveNode {
+  if (isSetNodeId(task.nodeId)) {
+    return { nodeId: task.nodeId, source: "task-override" };
+  }
+
+  if (isSetNodeId(settings.defaultNodeId)) {
+    return { nodeId: settings.defaultNodeId, source: "project-default" };
+  }
+
+  return { nodeId: undefined, source: "local" };
+}