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/Program.cs

@@ -8,6 +8,7 @@ using Microsoft.AspNetCore.HttpOverrides;
 using Microsoft.AspNetCore.ResponseCompression;
 using Microsoft.IdentityModel.Tokens;
 using MudBlazor.Services;
+using Serilog;
 using TaxBaik.Application;
 using TaxBaik.Application.Services;
 using TaxBaik.Infrastructure;
@@ -16,6 +17,20 @@ using TaxBaik.Web.Services;
 var builder = WebApplication.CreateBuilder(args);
 var isProduction = builder.Environment.IsProduction();
 
+// Serilog 설정
+builder.Host.UseSerilog((context, config) =>
+{
+    config
+        .MinimumLevel.Information()
+        .WriteTo.Console()
+        .WriteTo.File(
+            path: "logs/taxbaik-.log",
+            rollingInterval: RollingInterval.Day,
+            outputTemplate: "[{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz}] [{Level:u3}] {Message:lj}{NewLine}{Exception}")
+        .Enrich.FromLogContext()
+        .Enrich.WithProperty("Environment", context.HostingEnvironment.EnvironmentName);
+});
+
 // Controllers (API)
 builder.Services.AddControllers();
 builder.Services.AddProblemDetails();
@@ -72,6 +87,9 @@ builder.Services.AddAuthorizationCore();
 // Notifications (SignalR)
 builder.Services.AddScoped<INotificationService, NotificationService>();
 
+// Telegram Notification
+builder.Services.AddHttpClient<ITelegramNotificationService, TelegramNotificationService>();
+
 // HTTP Client for API (with automatic token refresh)
 builder.Services.AddScoped<ITokenStore, TokenStore>();
 builder.Services.AddScoped<TokenRefreshHandler>();
@@ -202,4 +220,39 @@ app.MapRazorComponents<TaxBaik.Web.Components.Admin.App>()
    .AddInteractiveServerRenderMode()
    .AllowAnonymous();
 
-app.Run();
+// 애플리케이션 시작/종료 로깅
+try
+{
+    Log.Information("애플리케이션 시작: {Environment}", app.Environment.EnvironmentName);
+    if (!app.Environment.IsDevelopment())
+    {
+        using (var scope = app.Services.CreateScope())
+        {
+            var telegramService = scope.ServiceProvider.GetRequiredService<ITelegramNotificationService>();
+            await telegramService.SendInfoAsync(
+                "서버 시작",
+                $"환경: {app.Environment.EnvironmentName}");
+        }
+    }
+    app.Run();
+}
+catch (Exception ex)
+{
+    Log.Fatal(ex, "애플리케이션 강종");
+    if (!app.Environment.IsDevelopment())
+    {
+        using (var scope = app.Services.CreateScope())
+        {
+            var telegramService = scope.ServiceProvider.GetRequiredService<ITelegramNotificationService>();
+            await telegramService.SendErrorAsync(
+                "서버 오류",
+                $"환경: {app.Environment.EnvironmentName}\n오류: {ex.Message}");
+        }
+    }
+    throw;
+}
+finally
+{
+    Log.Information("애플리케이션 종료");
+    Log.CloseAndFlush();
+}