feat: implement Razor Pages and static HTML login pages

Added two implementations of login page:
1. Razor Pages (Pages/Login.cshtml + Login.cshtml.cs)
   - Server-side rendering with form submission
   - Username remembering with cookies
   - Error handling and validation

2. Static HTML (wwwroot/login.html)
   - Pure HTML/CSS/JavaScript
   - Client-side form submission
   - LocalStorage for username persistence
   - Direct API call to /api/auth/login

Both implementations:
✅ Professional styling (dark theme, blur effects, primary blue buttons)
✅ Form validation
✅ Error message display
✅ ID persistence (LocalStorage/Cookies)
✅ Responsive design (mobile support)
✅ Integration with /api/auth/login endpoint

Technical notes:
- Blazor routing (@rendermode InteractiveServer) has limitations in .NET 10 Blazor Web App
- Razor Pages and static files are bypassed by Blazor's catch-all routing
- For production: recommend deploying login.html separately via nginx/reverse proxy
- Or use URL pattern like /user/login (outside Blazor's @page definitions)

Current workaround:
- Manually access: http://localhost:5265/login.html (works)
- API endpoint /api/auth/login is fully functional
- Ready for frontend deployment separation

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

tests/e2e/html-inspection.spec.ts

@@ -0,0 +1,32 @@
+import { test } from '@playwright/test';
+
+test('HTML 구조 검사', async ({ page }) => {
+  await page.goto('http://localhost:5265/login', { waitUntil: 'networkidle' });
+  await page.waitForTimeout(3000);
+
+  const html = await page.content();
+  
+  // 중요한 요소 확인
+  console.log('\n╔════════════════════════════════════════════════════╗');
+  console.log('║         HTML 구조 검사                             ║');
+  console.log('╚════════════════════════════════════════════════════╝\n');
+
+  console.log('🔍 주요 요소 검사:');
+  console.log(`   MudPaper 있음: ${html.includes('mud-paper') ? '✅' : '❌'}`);
+  console.log(`   MudTextField 있음: ${html.includes('mud-textfield') ? '✅' : '❌'}`);
+  console.log(`   login-container 있음: ${html.includes('login-container') ? '✅' : '❌'}`);
+  console.log(`   login-card 있음: ${html.includes('login-card') ? '✅' : '❌'}`);
+  console.log(`   form-input 있음: ${html.includes('form-input') ? '✅' : '❌'}`);
+  
+  console.log('\n📊 input 태그 개수:', (html.match(/<input/g) || []).length);
+  console.log('📊 button 태그 개수:', (html.match(/<button/g) || []).length);
+  
+  console.log('\n📝 Body 내용 샘플:');
+  const bodyMatch = html.match(/<body[^>]*>([\s\S]*?)<\/body>/i);
+  if (bodyMatch) {
+    const bodyContent = bodyMatch[1];
+    // 처음 500자만 출력 (정리된 형태)
+    const cleaned = bodyContent.replace(/\s+/g, ' ').substring(0, 600);
+    console.log(cleaned);
+  }
+});