refactor(frontend): decompose ConfigPage into dedicated config components

- Extract tab components: JailsTab, ActionsTab, FiltersTab, JailFilesTab,
  GlobalTab, ServerTab, ConfFilesTab, RegexTesterTab, MapTab, ExportTab
- Add form components: JailFileForm, ActionForm, FilterForm
- Add AutoSaveIndicator, RegexList, configStyles, and barrel index
- ConfigPage now composes these components; greatly reduces file size
- Add tests: ConfigPage.test.tsx, useAutoSave.test.ts

frontend/src/pages/__tests__/ConfigPage.test.tsx

@@ -0,0 +1,64 @@
+import { describe, it, expect, vi } from "vitest";
+import { render, screen, fireEvent } from "@testing-library/react";
+import { FluentProvider, webLightTheme } from "@fluentui/react-components";
+import { MemoryRouter } from "react-router-dom";
+import { ConfigPage } from "../ConfigPage";
+
+// Mock all tab components to avoid deep render trees and API calls.
+vi.mock("../../components/config", () => ({
+  JailsTab: () => <div data-testid="jails-tab">JailsTab</div>,
+  FiltersTab: () => <div data-testid="filters-tab">FiltersTab</div>,
+  ActionsTab: () => <div data-testid="actions-tab">ActionsTab</div>,
+  GlobalTab: () => <div data-testid="global-tab">GlobalTab</div>,
+  ServerTab: () => <div data-testid="server-tab">ServerTab</div>,
+  MapTab: () => <div data-testid="map-tab">MapTab</div>,
+  RegexTesterTab: () => <div data-testid="regex-tab">RegexTesterTab</div>,
+  ExportTab: () => <div data-testid="export-tab">ExportTab</div>,
+}));
+
+function renderPage() {
+  return render(
+    <MemoryRouter>
+      <FluentProvider theme={webLightTheme}>
+        <ConfigPage />
+      </FluentProvider>
+    </MemoryRouter>,
+  );
+}
+
+describe("ConfigPage", () => {
+  it("renders the Jails tab by default", () => {
+    renderPage();
+    expect(screen.getByTestId("jails-tab")).toBeInTheDocument();
+  });
+
+  it("switches to Filters tab when Filters tab is clicked", () => {
+    renderPage();
+    fireEvent.click(screen.getByRole("tab", { name: /filters/i }));
+    expect(screen.getByTestId("filters-tab")).toBeInTheDocument();
+    expect(screen.queryByTestId("jails-tab")).not.toBeInTheDocument();
+  });
+
+  it("switches to Actions tab when Actions tab is clicked", () => {
+    renderPage();
+    fireEvent.click(screen.getByRole("tab", { name: /actions/i }));
+    expect(screen.getByTestId("actions-tab")).toBeInTheDocument();
+  });
+
+  it("switches to Global tab when Global tab is clicked", () => {
+    renderPage();
+    fireEvent.click(screen.getByRole("tab", { name: /global/i }));
+    expect(screen.getByTestId("global-tab")).toBeInTheDocument();
+  });
+
+  it("switches to Server tab when Server tab is clicked", () => {
+    renderPage();
+    fireEvent.click(screen.getByRole("tab", { name: /server/i }));
+    expect(screen.getByTestId("server-tab")).toBeInTheDocument();
+  });
+
+  it("renders the page heading", () => {
+    renderPage();
+    expect(screen.getByRole("heading", { name: /configuration/i })).toBeInTheDocument();
+  });
+});