feat: normalize subscription architecture, integrate pgvector, and implement Stripe webhook subscription management.

src/NexusReader.Domain/Entities/NexusUser.cs

@@ -1,34 +1,49 @@
 using Microsoft.AspNetCore.Identity;
 using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
 
 namespace NexusReader.Domain.Entities;
 
-/// <summary>
-/// Extended Identity user for the Nexus AI E-Reader SaaS platform.
-/// </summary>
 public class NexusUser : IdentityUser
 {
     /// <summary>
-    /// Total number of AI tokens allowed for the current billing period.
+    /// User's display name or full name.
+    /// </summary>
+    [MaxLength(100)]
+    public string? DisplayName { get; set; }
+
+    /// <summary>
+    /// Total AI tokens available for the user (depends on subscription).
     /// </summary>
     public int AITokenLimit { get; set; }
 
     /// <summary>
-    /// Number of AI tokens consumed in the current billing period.
+    /// AI tokens consumed by the user in the current billing period.
     /// </summary>
     public int AITokensUsed { get; set; }
 
     /// <summary>
-    /// Unique identifier for the tenant (SaaS multi-tenancy support).
+    /// Date when the user last performed an AI-related action.
+    /// </summary>
+    public DateTime? LastAiActionDate { get; set; }
+
+    /// <summary>
+    /// Multi-tenant identifier.
     /// </summary>
     [Required]
     [MaxLength(128)]
     public string TenantId { get; set; } = "global";
 
     /// <summary>
-    /// Current subscription plan (e.g., "Free", "Pro", "Enterprise").
+    /// Foreign key for the current subscription plan.
     /// </summary>
-    public string CurrentPlan { get; set; } = "Free";
+    [Required]
+    public int SubscriptionPlanId { get; set; }
+
+    /// <summary>
+    /// Navigation property for the current subscription plan.
+    /// </summary>
+    public SubscriptionPlan? SubscriptionPlan { get; set; }
 
     /// <summary>
     /// Collection of e-books owned by the user.
@@ -43,10 +58,11 @@ public class NexusUser : IdentityUser
     /// <summary>
     /// ID of the last page read by the user.
     /// </summary>
+    [MaxLength(255)]
     public string? LastReadPageId { get; set; }
 
     /// <summary>
-    /// Timestamp of the last reading progress update.
+    /// Last read timestamp.
     /// </summary>
     public DateTime? LastReadAt { get; set; }
 }