feat: implement KM-RAG methodology artifacts and core architectural standards with supporting query and service updates

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

@@ -6,6 +6,7 @@ using Microsoft.Extensions.AI;
 using NexusReader.Application.DTOs.AI;
 using NexusReader.Application.Abstractions.Persistence;
 using Pgvector.EntityFrameworkCore;
+using System.Text.Json;
 
 namespace NexusReader.Application.Queries.Library;
 
@@ -88,7 +89,7 @@ public class SearchLibrarySemanticallyQueryHandler : IRequestHandler<SearchLibra
                     RelevanceScore = (float)(1 - c.Vector!.CosineDistance(queryVector)),
                     Metadata = string.IsNullOrEmpty(c.MetadataJson) 
                         ? null 
-                        : System.Text.Json.JsonSerializer.Deserialize<Dictionary<string, object>>(c.MetadataJson)
+                        : JsonSerializer.Deserialize<Dictionary<string, object>>(c.MetadataJson)
                 };
 
                 // Enrich snippet with definitions if present