fix: validate per-step fields before advancing Create Server wizard

- Add STEP_FIELDS constant mapping each step to its required fields
- Extract trigger() from useForm and call it on Next click
- Only advance to next step when trigger() returns true, blocking
  silent failures where invalid data could reach the Review step
- Add CreateServerPage.test.tsx with 8 tests covering step navigation,
  validation blocking, happy path, and submit mutation
- Update CLAUDE.md: mark /servers/new Complete, remove resolved bug
- Mark implementation plan as completed

frontend/src/__tests__/CreateServerPage.test.tsx

@@ -0,0 +1,197 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { MemoryRouter, Route, Routes } from "react-router-dom";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+import { CreateServerPage } from "@/pages/CreateServerPage";
+import { useCreateServer } from "@/hooks/useServers";
+import { useGamesList } from "@/hooks/useGames";
+import { useAuthStore } from "@/store/auth.store";
+import { useUIStore } from "@/store/ui.store";
+
+vi.mock("@/hooks/useServers", () => ({
+  useCreateServer: vi.fn(),
+}));
+
+vi.mock("@/hooks/useGames", () => ({
+  useGamesList: vi.fn(),
+}));
+
+vi.mock("@/store/auth.store", () => ({
+  useAuthStore: vi.fn(),
+}));
+
+vi.mock("@/store/ui.store", () => ({
+  useUIStore: vi.fn(),
+}));
+
+const mockMutateAsync = vi.fn();
+const mockAddNotification = vi.fn();
+
+function renderPage() {
+  const queryClient = new QueryClient({
+    defaultOptions: { queries: { retry: false } },
+  });
+
+  return {
+    user: userEvent.setup(),
+    ...render(
+      <QueryClientProvider client={queryClient}>
+        <MemoryRouter initialEntries={["/servers/new"]}>
+          <Routes>
+            <Route path="/servers/new" element={<CreateServerPage />} />
+            <Route path="/" element={<div>Dashboard</div>} />
+            <Route path="/servers/:id" element={<div>Server Detail</div>} />
+          </Routes>
+        </MemoryRouter>
+      </QueryClientProvider>,
+    ),
+  };
+}
+
+describe("CreateServerPage", () => {
+  beforeEach(() => {
+    vi.mocked(useAuthStore).mockReturnValue("admin");
+    vi.mocked(useUIStore).mockReturnValue(mockAddNotification);
+    vi.mocked(useGamesList).mockReturnValue({ data: undefined } as ReturnType<typeof useGamesList>);
+    vi.mocked(useCreateServer).mockReturnValue({
+      mutateAsync: mockMutateAsync,
+      isPending: false,
+    } as unknown as ReturnType<typeof useCreateServer>);
+    mockMutateAsync.mockReset();
+    mockAddNotification.mockReset();
+  });
+
+  it("renders step 0 (Game Type) by default", () => {
+    renderPage();
+    expect(screen.getByText("Create Server")).toBeInTheDocument();
+    expect(screen.getByRole("combobox")).toBeInTheDocument();
+    expect(screen.queryByPlaceholderText("My Arma Server")).not.toBeInTheDocument();
+  });
+
+  it("Next on step 0 advances to step 1", async () => {
+    const { user } = renderPage();
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => {
+      expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument();
+    });
+  });
+
+  it("Next on step 1 with empty name blocks advance and shows error", async () => {
+    const { user } = renderPage();
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument());
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+
+    await waitFor(() => {
+      expect(screen.getByText("Server name is required")).toBeInTheDocument();
+    });
+    expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument();
+  });
+
+  it("Next on step 1 with empty exe_path blocks advance and shows error", async () => {
+    const { user } = renderPage();
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument());
+
+    await user.type(screen.getByPlaceholderText("My Arma Server"), "Test Server");
+    await user.click(screen.getByRole("button", { name: /next/i }));
+
+    await waitFor(() => {
+      expect(screen.getByText("Executable path is required")).toBeInTheDocument();
+    });
+    expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument();
+  });
+
+  it("Next on step 1 with valid data advances to step 2", async () => {
+    const { user } = renderPage();
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument());
+
+    await user.type(screen.getByPlaceholderText("My Arma Server"), "My Server");
+    await user.type(
+      screen.getByPlaceholderText("D:/Arma3Server/arma3server_x64.exe"),
+      "C:/server/arma3.exe",
+    );
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+
+    await waitFor(() => {
+      expect(screen.getByLabelText(/auto-restart on crash/i)).toBeInTheDocument();
+    });
+  });
+
+  it("Back button on step 1 returns to step 0", async () => {
+    const { user } = renderPage();
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument());
+
+    await user.click(screen.getByRole("button", { name: /back/i }));
+
+    await waitFor(() => {
+      expect(screen.getByRole("combobox")).toBeInTheDocument();
+    });
+    expect(screen.queryByPlaceholderText("My Arma Server")).not.toBeInTheDocument();
+  });
+
+  it("full happy path reaches Review step", async () => {
+    const { user } = renderPage();
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument());
+
+    await user.type(screen.getByPlaceholderText("My Arma Server"), "My Server");
+    await user.type(
+      screen.getByPlaceholderText("D:/Arma3Server/arma3server_x64.exe"),
+      "C:/server/arma3.exe",
+    );
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByLabelText(/auto-restart on crash/i)).toBeInTheDocument());
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => {
+      expect(screen.getByText("Review Configuration")).toBeInTheDocument();
+    });
+    expect(screen.getByRole("button", { name: /create server/i })).toBeInTheDocument();
+  });
+
+  it("submit fires createServer mutation on valid data", async () => {
+    mockMutateAsync.mockResolvedValueOnce({ data: { id: 42 } });
+
+    const { user } = renderPage();
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByPlaceholderText("My Arma Server")).toBeInTheDocument());
+
+    await user.type(screen.getByPlaceholderText("My Arma Server"), "My Server");
+    await user.type(
+      screen.getByPlaceholderText("D:/Arma3Server/arma3server_x64.exe"),
+      "C:/server/arma3.exe",
+    );
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByLabelText(/auto-restart on crash/i)).toBeInTheDocument());
+
+    await user.click(screen.getByRole("button", { name: /next/i }));
+    await waitFor(() => expect(screen.getByText("Review Configuration")).toBeInTheDocument());
+
+    await user.click(screen.getByRole("button", { name: /create server/i }));
+
+    await waitFor(() => {
+      expect(mockMutateAsync).toHaveBeenCalledWith(
+        expect.objectContaining({
+          name: "My Server",
+          exe_path: "C:/server/arma3.exe",
+          game_type: "arma3",
+        }),
+      );
+    });
+  });
+});