fix(FN-2444): polish node dashboard UX and discovery core handling

- Update node management UI components to use shared form/button classes, semantic color tokens, and accessible interactions
- Refine mesh topology rendering and related dashboard tests for improved readability and behavior coverage
- Adjust discovery routes to reuse injected centralCore instances without unnecessary init/close cycles
- Add/extend tests for shared CentralCore discovery flows and model settings scope save behavior

packages/dashboard/src/__tests__/routes-diff.test.ts

@@ -103,7 +103,7 @@ describe("GET /api/tasks/:id/diff", () => {
     const response = await requestDiff(app, "NONEXISTENT");
 
     expect(response.status).toBe(404);
-  });
+  }, 15_000);
 
   it("handler can be created with valid task", async () => {
     const store = new MockStore();