chore: finish frontend ESLint migration #18

Enable every plugin recommended preset and replace Biome with ESLint formatting.

Preserve API contracts and JSX whitespace; verify source, tests, builds and tooling.

src/app/ui/AppBreadcrumbs/AppBreadcrumbs.test.tsx

@@ -2,6 +2,7 @@ import { MantineProvider } from "@mantine/core";
 import { render, screen, within } from "@testing-library/react";
 import { MemoryRouter } from "react-router";
 import { afterEach, describe, expect, it, vi } from "vitest";
+
 import { AppBreadcrumbs } from "./AppBreadcrumbs";
 
 const { useBrokerageAccounts } = vi.hoisted(() => ({