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/Catalog.cshtml.cs

@@ -0,0 +1,84 @@
+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 CatalogModel : PageModel
+{
+    private readonly RR3DbContext _context;
+
+    public CatalogModel(RR3DbContext context)
+    {
+        _context = context;
+    }
+
+    public List<CatalogItem> CatalogItems { get; set; } = new();
+
+    public async Task OnGetAsync()
+    {
+        CatalogItems = await _context.CatalogItems
+            .OrderBy(c => c.Type)
+            .ThenBy(c => c.Name)
+            .ToListAsync();
+    }
+
+    public async Task<IActionResult> OnPostAddAsync(string sku, string name, string type, decimal price, bool available)
+    {
+        var item = new CatalogItem
+        {
+            Sku = sku,
+            Name = name,
+            Type = type,
+            Price = price,
+            Available = available
+        };
+
+        _context.CatalogItems.Add(item);
+        await _context.SaveChangesAsync();
+
+        return RedirectToPage();
+    }
+
+    public async Task<IActionResult> OnPostUpdateAsync(int itemId, string sku, string name, string type, decimal price, bool available)
+    {
+        var item = await _context.CatalogItems.FindAsync(itemId);
+        if (item != null)
+        {
+            item.Sku = sku;
+            item.Name = name;
+            item.Type = type;
+            item.Price = price;
+            item.Available = available;
+            await _context.SaveChangesAsync();
+        }
+
+        return RedirectToPage();
+    }
+
+    public async Task<IActionResult> OnPostToggleAvailabilityAsync(int itemId)
+    {
+        var item = await _context.CatalogItems.FindAsync(itemId);
+        if (item != null)
+        {
+            item.Available = !item.Available;
+            await _context.SaveChangesAsync();
+        }
+
+        return RedirectToPage();
+    }
+
+    public async Task<IActionResult> OnPostDeleteAsync(int itemId)
+    {
+        var item = await _context.CatalogItems.FindAsync(itemId);
+        if (item != null)
+        {
+            _context.CatalogItems.Remove(item);
+            await _context.SaveChangesAsync();
+        }
+
+        return RedirectToPage();
+    }
+}