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

src/NexusReader.Domain/Entities/Ebook.cs

@@ -23,6 +23,10 @@ public class Ebook
 
     public string? CoverUrl { get; set; }
 
+    [Required]
+    [MaxLength(128)]
+    public string TenantId { get; set; } = "global";
+
     public DateTime AddedDate { get; set; } = DateTime.UtcNow;
 
     public DateTime? LastReadDate { get; set; }

src/NexusReader.Domain/Entities/KnowledgeUnit.cs

@@ -1,6 +1,7 @@
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
 using NexusReader.Domain.Enums;
+using Pgvector;
 
 namespace NexusReader.Domain.Entities;
 
@@ -30,8 +31,7 @@ public class KnowledgeUnit
     [MaxLength(128)]
     public string TenantId { get; set; } = string.Empty;
 
-    [Column(TypeName = "vector(768)")] // Default for text-embedding-004
-    public float[]? Vector { get; set; }
+    public Vector? Vector { get; set; }
 
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
 

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; }
 }

src/NexusReader.Domain/Entities/QuizResult.cs

@@ -17,6 +17,10 @@ public class QuizResult
     [ForeignKey(nameof(UserId))]
     public NexusUser? User { get; set; }
 
+    [Required]
+    [MaxLength(128)]
+    public string TenantId { get; set; } = "global";
+
     [Required]
     public string Topic { get; set; } = string.Empty;
 

src/NexusReader.Domain/Entities/SemanticKnowledgeCache.cs

@@ -1,5 +1,6 @@
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
+using Pgvector;
 
 namespace NexusReader.Domain.Entities;
 
@@ -27,8 +28,7 @@ public class SemanticKnowledgeCache
     [MaxLength(128)]
     public string TenantId { get; set; } = string.Empty;
 
-    [Column(TypeName = "vector(1536)")] // text-embedding-004 has 768 or 1536 dims, assuming 1536 for high-fidelity
-    public float[]? Vector { get; set; }
+    public Vector? Vector { get; set; }
 
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
 }

src/NexusReader.Domain/Entities/SubscriptionPlan.cs

@@ -0,0 +1,30 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace NexusReader.Domain.Entities;
+
+public class SubscriptionPlan
+{
+    public const string FreeName = "Free";
+    public const string BasicName = "Basic";
+    public const string ProName = "Pro";
+    public const string EnterpriseName = "Enterprise";
+
+    public const int FreeId = 1;
+    public const int BasicId = 2;
+    public const int ProId = 3;
+    public const int EnterpriseId = 4;
+
+    [Key]
+    public int Id { get; set; }
+
+    [Required]
+    [MaxLength(50)]
+    public string PlanName { get; set; } = string.Empty;
+
+    public int AITokenLimit { get; set; }
+
+    public decimal MonthlyPrice { get; set; }
+
+    [MaxLength(50)]
+    public string StripeProductId { get; set; } = string.Empty;
+}