Initial commit: RR3 Community Server with web admin panel

- ASP.NET Core 8 REST API server
- 12 API endpoints matching EA Synergy protocol
- SQLite database with Entity Framework Core
- Web admin panel with Bootstrap 5
- User, Catalog, Session, Purchase management
- Comprehensive documentation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

RR3CommunityServer/Pages/Sessions.cshtml.cs

@@ -0,0 +1,56 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using Microsoft.EntityFrameworkCore;
+using RR3CommunityServer.Data;
+using static RR3CommunityServer.Data.RR3DbContext;
+
+namespace RR3CommunityServer.Pages;
+
+public class SessionsModel : PageModel
+{
+    private readonly RR3DbContext _context;
+
+    public SessionsModel(RR3DbContext context)
+    {
+        _context = context;
+    }
+
+    public List<Session> AllSessions { get; set; } = new();
+    public List<Session> ActiveSessions { get; set; } = new();
+    public List<Session> ExpiredSessions { get; set; } = new();
+
+    public async Task OnGetAsync()
+    {
+        AllSessions = await _context.Sessions
+            .OrderByDescending(s => s.CreatedAt)
+            .ToListAsync();
+
+        var now = DateTime.UtcNow;
+        ActiveSessions = AllSessions.Where(s => s.ExpiresAt > now).ToList();
+        ExpiredSessions = AllSessions.Where(s => s.ExpiresAt <= now).ToList();
+    }
+
+    public async Task<IActionResult> OnPostDeleteAsync(int sessionId)
+    {
+        var session = await _context.Sessions.FindAsync(sessionId);
+        if (session != null)
+        {
+            _context.Sessions.Remove(session);
+            await _context.SaveChangesAsync();
+        }
+
+        return RedirectToPage();
+    }
+
+    public async Task<IActionResult> OnPostCleanupExpiredAsync()
+    {
+        var expiredSessions = await _context.Sessions
+            .Where(s => s.ExpiresAt <= DateTime.UtcNow)
+            .ToListAsync();
+
+        _context.Sessions.RemoveRange(expiredSessions);
+        await _context.SaveChangesAsync();
+
+        return RedirectToPage();
+    }
+}