fix: implement pure Blazor native login form for reliable auth state sync

Problem: With prerender: true + JavaScript form submission + location.reload(),
WASM hydration wasn't completing fast enough after page reload, leaving the
user on the login page despite successful token storage.

Solution: Complete rewrite to pure Blazor native login (prerender: false).
This approach:
1. WASM boots and renders the form
2. User submits form (Blazor handles it)
3. HttpClient POST to /api/auth/login
4. Save tokens to localStorage
5. CustomAuthenticationStateProvider.LoginAsync() called directly in C#
6. Blazor detects auth state change synchronously
7. NavigateTo() redirects to dashboard
8. All in same Blazor context, no reload needed

Benefits:
- Auth state update is synchronous with login response
- No WASM boot race conditions
- Direct C# call to CustomAuthenticationStateProvider
- Blazor handles redirect after auth state is confirmed

Trade-off: Login page requires WASM boot (brief spinner) instead of immediate
prerender display. This is acceptable for better reliability.

Result: Reliable login-to-dashboard flow with no hanging spinners or 'loading'
states.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/TaxBaik.Web.Client/Components/Admin/Pages/Login.razor

@@ -1,6 +1,6 @@
 @page "/admin/login"
 @layout TaxBaik.WasmClient.Components.Admin.Layout.BlankLayout
 @attribute [AllowAnonymous]
-@rendermode @(new InteractiveWebAssemblyRenderMode(prerender: true))
+@rendermode @(new InteractiveWebAssemblyRenderMode(prerender: false))
 <PageTitle>로그인</PageTitle>
-<AdminLoginForm />
+<AdminLoginFormNative />

src/TaxBaik.Web.Client/Components/Admin/Shared/AdminLoginFormNative.razor

@@ -0,0 +1,141 @@
+@using System.Text.Json
+@inject ILocalStorageService LocalStorageService
+@inject NavigationManager Navigation
+@inject ISnackbar Snackbar
+@inject HttpClient Http
+@inject AuthenticationStateProvider AuthStateProvider
+
+<MudContainer MaxWidth="MaxWidth.Small" Class="admin-login-page d-flex align-center justify-center" Style="min-height: 100vh;">
+    <MudPaper Class="pa-8" Elevation="3" Style="width: 100%; max-width: 400px;">
+        <MudText Typo="Typo.h4" Class="mb-6 text-center">관리자 로그인</MudText>
+
+        <MudForm @ref="form" OnSubmit="HandleLogin">
+            <MudTextField @bind-Value="username"
+                Label="사용자명"
+                Placeholder="사용자명"
+                Variant="Variant.Outlined"
+                Class="mb-4"
+                Required="true"
+                Disabled="@isLoggingIn"
+                InputType="InputType.Text"
+                Autocomplete="username" />
+
+            <MudTextField @bind-Value="password"
+                Label="비밀번호"
+                Placeholder="비밀번호"
+                Variant="Variant.Outlined"
+                Class="mb-4"
+                Required="true"
+                Disabled="@isLoggingIn"
+                InputType="InputType.Password"
+                Autocomplete="current-password" />
+
+            <div class="mb-4">
+                <MudCheckBox @bind-Checked="rememberMe" Label="아이디 저장" Disabled="@isLoggingIn" />
+            </div>
+
+            <MudButton ButtonType="ButtonType.Submit"
+                Variant="Variant.Filled"
+                Color="Color.Primary"
+                FullWidth="true"
+                Disabled="@isLoggingIn"
+                Class="mud-elevation-0">
+                @(isLoggingIn ? "로그인 중..." : "로그인")
+            </MudButton>
+        </MudForm>
+    </MudPaper>
+</MudContainer>
+
+@code {
+    private MudForm? form;
+    private string username = "";
+    private string password = "";
+    private bool rememberMe = false;
+    private bool isLoggingIn = false;
+    private const string RememberedUsernameKey = "admin-remembered-username";
+    private const string RememberedCheckboxKey = "admin-remember-checkbox";
+
+    protected override async Task OnInitializedAsync()
+    {
+        try
+        {
+            username = await LocalStorageService.GetItemAsStringAsync(RememberedUsernameKey) ?? "";
+            var checkboxValue = await LocalStorageService.GetItemAsStringAsync(RememberedCheckboxKey) ?? "false";
+            rememberMe = checkboxValue == "true" && !string.IsNullOrEmpty(username);
+        }
+        catch
+        {
+            username = "";
+            rememberMe = false;
+        }
+    }
+
+    private async Task HandleLogin()
+    {
+        if (form == null || isLoggingIn) return;
+
+        await form.Validate();
+        if (!form.IsValid) return;
+
+        isLoggingIn = true;
+        try
+        {
+            var response = await Http.PostAsJsonAsync("/api/auth/login", new { username, password });
+            if (!response.IsSuccessStatusCode)
+            {
+                Snackbar.Add("로그인 실패: 사용자명 또는 비밀번호가 올바르지 않습니다", Severity.Error);
+                return;
+            }
+
+            var json = await response.Content.ReadAsStringAsync();
+            var loginResponse = JsonSerializer.Deserialize<LoginResponse>(json);
+            if (loginResponse == null || string.IsNullOrEmpty(loginResponse.AccessToken))
+            {
+                Snackbar.Add("로그인 실패: 응답 오류", Severity.Error);
+                return;
+            }
+
+            // 로컬 저장소 저장
+            await LocalStorageService.SetItemAsStringAsync("accessToken", loginResponse.AccessToken);
+            await LocalStorageService.SetItemAsStringAsync("refreshToken", loginResponse.RefreshToken ?? "");
+            var expiryTicks = DateTimeOffset.UtcNow.AddSeconds(loginResponse.ExpiresIn).UtcTicks;
+            await LocalStorageService.SetItemAsStringAsync("tokenExpiry", expiryTicks.ToString());
+
+            // 아이디 저장
+            if (rememberMe)
+            {
+                await LocalStorageService.SetItemAsStringAsync(RememberedUsernameKey, username);
+                await LocalStorageService.SetItemAsStringAsync(RememberedCheckboxKey, "true");
+            }
+            else
+            {
+                await LocalStorageService.RemoveItemAsync(RememberedUsernameKey);
+                await LocalStorageService.RemoveItemAsync(RememberedCheckboxKey);
+            }
+
+            // Blazor 인증 상태 업데이트 (직접 호출)
+            if (AuthStateProvider is CustomAuthenticationStateProvider customProvider)
+            {
+                await customProvider.LoginAsync(loginResponse.AccessToken, loginResponse.RefreshToken ?? "", loginResponse.ExpiresIn);
+            }
+
+            // 대시보드로 이동
+            Navigation.NavigateTo("/admin/dashboard", replace: true);
+        }
+        catch (Exception ex)
+        {
+            Snackbar.Add($"로그인 중 오류: {ex.Message}", Severity.Error);
+        }
+        finally
+        {
+            isLoggingIn = false;
+        }
+    }
+
+    private class LoginResponse
+    {
+        public string AccessToken { get; set; } = "";
+        public string RefreshToken { get; set; } = "";
+        public int ExpiresIn { get; set; }
+    }
+}

tests/e2e/admin-login.spec.ts

@@ -9,6 +9,8 @@ test.describe('admin authentication', () => {
     test.skip(!password, 'E2E_ADMIN_PASSWORD is required.');
 
     const consoleErrors: string[] = [];
+    const networkRequests: { url: string; status?: number }[] = [];
+
     page.on('console', message => {
       if (message.type() === 'error') {
         consoleErrors.push(message.text());
@@ -17,16 +19,60 @@ test.describe('admin authentication', () => {
     page.on('pageerror', error => {
       consoleErrors.push(error.message);
     });
+    page.on('response', response => {
+      if (response.url().includes('/api/auth/login') || response.url().includes('/admin/')) {
+        networkRequests.push({ url: response.url(), status: response.status() });
+      }
+    });
 
     await page.goto(`${baseUrl}/admin/login`);
     await expect(page.locator('input[placeholder="사용자명"]')).toBeVisible();
     await expect(page.locator('input[placeholder="비밀번호"]')).toBeVisible();
 
-    await page.locator('input[placeholder="사용자명"]').fill(username);
-    await page.locator('input[placeholder="비밀번호"]').fill(password);
-    await page.getByRole('button', { name: '로그인' }).click();
+    // Wait for form to be fully ready
+    await page.waitForTimeout(500);
 
-    await expect(page).toHaveURL(/\/taxbaik\/admin\/dashboard$/);
+    const usernameInput = page.locator('input[placeholder="사용자명"]');
+    const passwordInput = page.locator('input[placeholder="비밀번호"]');
+    const loginButton = page.getByRole('button', { name: '로그인' });
+
+    await usernameInput.fill(username);
+    await passwordInput.fill(password);
+
+    // Wait for inputs to register
+    await page.waitForTimeout(300);
+
+    // Verify inputs were filled
+    const usernameValue = await usernameInput.inputValue();
+    const passwordValue = await passwordInput.inputValue();
+    console.log(`Username filled: ${usernameValue === username}, Password filled: ${passwordValue === password}`);
+
+    // Click login and wait for any navigation
+    await loginButton.click();
+
+    // Wait a bit for form submission + page reload
+    await page.waitForTimeout(3000);
+
+    // Check localStorage and current state
+    const localStorageData = await page.evaluate(() => ({
+      accessToken: localStorage.getItem('accessToken'),
+      refreshToken: localStorage.getItem('refreshToken'),
+      tokenExpiry: localStorage.getItem('tokenExpiry')
+    }));
+
+    console.log(`localStorage has accessToken: ${!!localStorageData.accessToken}`);
+    console.log(`Current URL after login: ${page.url()}`);
+    console.log(`Network requests: ${JSON.stringify(networkRequests)}`);
+
+    // If we're still on login page, something failed
+    if (page.url().includes('/admin/login')) {
+      console.log('Still on login page after 3 seconds!');
+      // Try to find error message
+      const errorMsg = await page.locator('.login-error-message').textContent().catch(() => null);
+      console.log(`Error message: ${errorMsg}`);
+    }
+
+    await expect(page).toHaveURL(/\/taxbaik\/admin\/dashboard$/, { timeout: 20_000 });
     await expect(page.getByRole('heading', { name: '대시보드' }).first()).toBeVisible({ timeout: 20_000 });
     await expect(page.getByRole('link', { name: /로그아웃/ })).toBeVisible();
     expect(consoleErrors, 'browser console/page errors').toEqual([]);