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>

TaxBaik.Web/appsettings.json

@@ -18,8 +18,8 @@
     "BaseUrl": "http://localhost:5001/taxbaik/api/"
   },
   "Telegram": {
-    "BotToken": "",
-    "ChatId": ""
+    "BotToken": "8679990909:AAGLLRUIAuEbYAZVGOYDu-UuTu4ihroEiX0",
+    "ChatId": "-5585148480"
   },
   "Admin": {
     "PasswordResetToken": "dev-reset-token-12345"