feat(FN-3193): split-pane redesign of agents workspace with mobile support

Merges FN-3122's agents workspace redesign (split-pane layout, mobile responsiveness) and FN-3193's test infrastructure stabilization. The AgentsView and AgentDetailView components received major style and layout updates, with corresponding test coverage added. Several vitest config entries were con

Fusion-Task-Id: FN-3193

packages/engine/src/__tests__/hermes-runtime-e2e.test.ts

@@ -36,12 +36,6 @@ vi.mock("../logger.js", () => ({
   },
 }));
 
-vi.mock("@fusion/engine", () => ({
-  createFnAgent: mockCreateFnAgent,
-  promptWithFallback: mockPromptWithFallback,
-  describeModel: mockDescribeModel,
-}));
-
 vi.mock("@mariozechner/pi-ai", () => ({
   getModel: mockGetModel,
   streamSimple: mockStreamSimple,