feat(FN-3044): add canonical mock helpers and migrate representative test s

This merge introduces canonical mock helper modules across the dashboard and engine packages, and migrates representative test suites to use them for consistency. The changes add four new mock helpers (`mockApi.ts`, `mockLucide.ts`, `mockCore.ts`, `mockCoreEngine.ts`) and harden the API mock proxy's

Fusion-Task-Id: FN-3044

packages/dashboard/src/test/mockCoreEngine.ts

@@ -0,0 +1,27 @@
+/**
+ * Canonical @fusion/core and @fusion/engine mock helpers for dashboard server tests.
+ *
+ * Add new mocked exports here first before duplicating large per-suite mock objects.
+ */
+import { vi } from "vitest";
+
+type AnyModule = Record<string, unknown>;
+
+export async function createCoreMock(
+  importActual: () => Promise<AnyModule>,
+  overrides: AnyModule = {},
+): Promise<AnyModule> {
+  const actual = await importActual();
+  return {
+    ...actual,
+    ...overrides,
+  };
+}
+
+export function createEngineMock(overrides: AnyModule = {}): AnyModule {
+  return {
+    createFnAgent: vi.fn(),
+    promptWithFallback: vi.fn(),
+    ...overrides,
+  };
+}