feat: integrate Serilog and Telegram notifications

- Add Serilog for structured logging (Console + File)
- Implement TelegramNotificationService for admin alerts
- Log successful/failed login attempts with Telegram notifications
- Add application startup/shutdown logging
- Log important events to Telegram Chat ID: -5585148480
- Configuration: Telegram:BotToken and Telegram:ChatId in appsettings

Features:
- Automatic daily log rotation
- Structured logging with timestamps
- Environment-aware alerts
- Error and info level Telegram messages

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

debug-settings.js

@@ -0,0 +1,57 @@
+import { chromium } from '@playwright/test';
+
+const browser = await chromium.launch();
+const page = await browser.newPage();
+
+try {
+  // 1. 로그인
+  console.log('🔓 로그인 중...');
+  await page.goto('http://178.104.200.7/taxbaik/admin/login', { waitUntil: 'networkidle' });
+  await page.fill('input[placeholder="사용자명"]', 'test_admin');
+  await page.fill('input[placeholder="비밀번호"]', 'TestAdmin@123456');
+  await page.click('button:has-text("로그인")');
+  await page.waitForURL(/\/taxbaik\/admin\/dashboard$/, { timeout: 10000 });
+  console.log('✅ 로그인 성공');
+
+  // 2. Settings 페이지로 이동
+  console.log('\n📍 Settings 페이지로 이동...');
+  await page.goto('http://178.104.200.7/taxbaik/admin/settings', { waitUntil: 'domcontentloaded' });
+  
+  // 3. 다양한 대기 전략 시도
+  console.log('⏳ 페이지 로드 대기 중...');
+  
+  for (let i = 1; i <= 5; i++) {
+    await page.waitForTimeout(1000);
+    const title = await page.locator('h4:has-text("설정")').count();
+    const body = await page.locator('body').evaluate(el => el.innerHTML.length);
+    const mudComponents = await page.locator('[class*="mud-"]').count();
+    
+    console.log(`시도 ${i}: body=${body}bytes, mud=${mudComponents}, title=${title}`);
+    
+    if (mudComponents > 10 && body > 5000) {
+      console.log('✅ 페이지 렌더링 감지됨!');
+      break;
+    }
+  }
+  
+  // 4. 최종 상태 확인
+  console.log('\n📊 최종 상태:');
+  const hasContent = await page.locator('body').evaluate(el => el.innerText.length > 100);
+  const hasComponents = await page.locator('[class*="mud-"]').count();
+  
+  console.log(`- 텍스트 콘텐츠: ${hasContent ? '있음' : '없음'}`);
+  console.log(`- MudBlazor 컴포넌트: ${hasComponents}개`);
+  
+  if (!hasContent) {
+    console.log('\n❌ Settings 페이지 렌더링 실패');
+    console.log('HTML 스니펫:');
+    const html = await page.content();
+    const bodyMatch = html.match(/<body[^>]*>([\s\S]{0,500})/);
+    if (bodyMatch) console.log(bodyMatch[1]);
+  }
+  
+} catch (error) {
+  console.error('❌ 에러:', error.message);
+}
+
+await browser.close();