Add admin panel authentication and login system

Features:
- Login page with username/email + password
- Registration page for new accounts
- Logout functionality
- Cookie-based authentication (30-day sessions)
- Auto-redirect to login for unauthorized access
- User dropdown in navbar with logout link

Security:
- All admin pages now require authentication
- [Authorize] attribute on all admin PageModels
- Redirect to /Login if not authenticated
- Auto-login after registration

UI:
- Beautiful gradient login/register pages
- Consistent styling with admin panel
- User info displayed in navbar
- Logout link in dropdown menu

Starting resources for new users:
- 100,000 Gold
- 500,000 Cash
- Level 1
- Full admin panel access

Ready for production deployment!

RR3CommunityServer/Program.cs

@@ -1,4 +1,5 @@
 using Microsoft.EntityFrameworkCore;
+using Microsoft.AspNetCore.Authentication.Cookies;
 using RR3CommunityServer.Data;
 using RR3CommunityServer.Services;
 using RR3CommunityServer.Middleware;
@@ -8,6 +9,20 @@ var builder = WebApplication.CreateBuilder(args);
 // Add services to the container
 builder.Services.AddControllers();
 builder.Services.AddRazorPages(); // Add Razor Pages support
+
+// Add cookie authentication
+builder.Services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
+    .AddCookie(options =>
+    {
+        options.LoginPath = "/Login";
+        options.LogoutPath = "/Logout";
+        options.AccessDeniedPath = "/Login";
+        options.ExpireTimeSpan = TimeSpan.FromDays(30);
+        options.SlidingExpiration = true;
+    });
+
+builder.Services.AddAuthorization();
+
 builder.Services.AddEndpointsApiExplorer();
 builder.Services.AddSwaggerGen();
 
@@ -53,16 +68,19 @@ using (var scope = app.Services.CreateScope())
 app.UseHttpsRedirection();
 app.UseCors();
 
+// Authentication & Authorization
+app.UseAuthentication();
+app.UseAuthorization();
+
 // Custom middleware
 app.UseMiddleware<SynergyHeadersMiddleware>();
 app.UseMiddleware<SessionValidationMiddleware>();
 
-app.UseAuthorization();
 app.MapControllers();
 app.MapRazorPages(); // Add Razor Pages routing
 
-// Redirect root to admin panel
-app.MapGet("/", () => Results.Redirect("/admin"));
+// Redirect root to login page
+app.MapGet("/", () => Results.Redirect("/Login"));
 
 Console.WriteLine("╔══════════════════════════════════════════════════════════╗");
 Console.WriteLine("║      Real Racing 3 Community Server - RUNNING          ║");