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/TaxBaik.Web.csproj

@@ -17,6 +17,9 @@
     <PackageReference Include="System.IdentityModel.Tokens.Jwt" Version="8.19.1" />
     <PackageReference Include="Microsoft.IdentityModel.Tokens" Version="8.19.1" />
     <PackageReference Include="Microsoft.AspNetCore.Authentication.JwtBearer" Version="10.0.9" />
+    <PackageReference Include="Serilog.AspNetCore" Version="8.0.1" />
+    <PackageReference Include="Serilog.Sinks.Console" Version="6.0.0" />
+    <PackageReference Include="Serilog.Sinks.File" Version="5.0.0" />
   </ItemGroup>
 
 </Project>