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

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