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>

tests/e2e/dashboard-check.spec.ts

@@ -0,0 +1,50 @@
+import { test } from '@playwright/test';
+
+test('check dashboard metrics', async ({ page }) => {
+  const baseUrl = 'http://178.104.200.7/taxbaik';
+
+  // Login
+  await page.goto(`${baseUrl}/admin/login`);
+  await page.fill('input[placeholder="사용자명"]', 'test_admin');
+  await page.fill('input[placeholder="비밀번호"]', 'TestAdmin@123456');
+  await page.click('button[type="submit"]');
+  await page.waitForURL(/admin\/dashboard/);
+
+  // Wait for page load
+  await page.waitForSelector('.admin-page-hero', { timeout: 5000 });
+  await page.waitForTimeout(2000);
+
+  // Check for metric cards
+  const metrics = page.locator('.admin-metric-card');
+  const metricCount = await metrics.count();
+  console.log(`\nFound ${metricCount} metric cards`);
+
+  // Log each metric value
+  for (let i = 0; i < Math.min(metricCount, 4); i++) {
+    const metric = metrics.nth(i);
+    const text = await metric.textContent();
+    console.log(`  Metric ${i + 1}: ${text?.trim().slice(0, 100)}`);
+  }
+
+  // Check for data in main content area
+  const contentText = await page.locator('body').textContent();
+  const has총문의 = contentText?.includes('총 문의') || false;
+  const has신규문의 = contentText?.includes('신규 문의') || false;
+  const has활성공지 = contentText?.includes('활성 공지') || false;
+  const has예정세무신고 = contentText?.includes('예정 세무신고') || false;
+
+  console.log(`\nDashboard content check:`);
+  console.log(`  - 총 문의: ${has총문의}`);
+  console.log(`  - 신규 문의: ${has신규문의}`);
+  console.log(`  - 활성 공지: ${has활성공지}`);
+  console.log(`  - 예정 세무신고: ${has예정세무신고}`);
+
+  // Try to get text content from specific areas
+  const dashContent = await page.locator('.admin-content').textContent();
+  if (dashContent) {
+    console.log(`\nDashboard content length: ${dashContent.length}`);
+    // Check if there are numbers
+    const numbers = dashContent.match(/\d+/g) || [];
+    console.log(`Numbers found: ${numbers.slice(0, 10).join(', ')}`);
+  }
+});