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

src/NexusReader.Application/DTOs/User/SubscriptionPlanDto.cs

@@ -0,0 +1,9 @@
+namespace NexusReader.Application.DTOs.User;
+
+public record SubscriptionPlanDto
+{
+    public int Id { get; init; }
+    public string Name { get; init; } = string.Empty;
+    public int AITokenLimit { get; init; }
+    public decimal MonthlyPrice { get; init; }
+}

src/NexusReader.Application/DTOs/User/UserProfileDto.cs

@@ -0,0 +1,25 @@
+namespace NexusReader.Application.DTOs.User;
+
+public record UserProfileDto
+{
+    public string Email { get; init; } = string.Empty;
+    public int AITokensUsed { get; init; }
+    
+    /// <summary>
+    /// Relational data for the current subscription plan.
+    /// </summary>
+    public SubscriptionPlanDto Plan { get; init; } = new();
+
+    public int AverageQuizScore { get; init; }
+    
+    /// <summary>
+    /// Summary of the last read book.
+    /// </summary>
+    public LastReadBookDto? LastReadBook { get; init; }
+}
+
+public record LastReadBookDto
+{
+    public Guid Id { get; init; }
+    public string Title { get; init; } = string.Empty;
+}

src/NexusReader.Application/Queries/Library/SearchLibrarySemanticallyQuery.cs

@@ -5,6 +5,7 @@ using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.AI;
 using NexusReader.Application.DTOs.AI;
 using NexusReader.Application.Abstractions.Persistence;
+using Pgvector;
 using Pgvector.EntityFrameworkCore;
 using System.Text.Json;
 
@@ -37,7 +38,7 @@ public class SearchLibrarySemanticallyQueryHandler : IRequestHandler<SearchLibra
         {
             // 1. Generate embedding for user query
             var embeddingResponse = await _embeddingGenerator.GenerateAsync(new[] { request.QueryText }, cancellationToken: cancellationToken);
-            var queryVector = embeddingResponse.First().Vector.ToArray();
+            var queryVector = new Vector(embeddingResponse.First().Vector.ToArray());
 
             // 2. Perform Cosine Similarity Search on Knowledge Units
             var candidates = await _dbContext.KnowledgeUnits

src/NexusReader.Application/Security/Authorization/ProUserHandler.cs

@@ -31,7 +31,7 @@ public class ProUserHandler : AuthorizationHandler<ProUserRequirement>
         }
 
         // Rule 1: Explicit Pro plan
-        if (user.CurrentPlan == "Pro")
+        if (user.SubscriptionPlanId == SubscriptionPlan.ProId)
         {
             context.Succeed(requirement);
             return;