refactor: consolidate project structure by migrating authentication, identity, and shared UI components while removing legacy Web Client files.

src/NexusReader.Infrastructure/Identity/TokenLimitHandler.cs

@@ -0,0 +1,45 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Identity;
+using NexusReader.Domain.Entities;
+using NexusReader.Infrastructure.Persistence;
+
+namespace NexusReader.Infrastructure.Identity;
+
+/// <summary>
+/// Handler that validates if the user has available AI tokens.
+/// </summary>
+public class TokenLimitHandler : AuthorizationHandler<TokenLimitRequirement>
+{
+    private readonly AppDbContext _dbContext;
+    private readonly UserManager<NexusUser> _userManager;
+
+    public TokenLimitHandler(AppDbContext dbContext, UserManager<NexusUser> userManager)
+    {
+        _dbContext = dbContext;
+        _userManager = userManager;
+    }
+
+    protected override async Task HandleRequirementAsync(
+        AuthorizationHandlerContext context,
+        TokenLimitRequirement requirement)
+    {
+        var userId = context.User.FindFirstValue(ClaimTypes.NameIdentifier);
+        if (userId == null)
+        {
+            return;
+        }
+
+        var user = await _userManager.FindByIdAsync(userId);
+        if (user == null)
+        {
+            return;
+        }
+
+        // Check if user has available tokens
+        if (user.AITokensUsed < user.AITokenLimit)
+        {
+            context.Succeed(requirement);
+        }
+    }
+}