feat(ui): implement premium NexusSearchBox component and integrate semantic search navigation

src/NexusReader.Data/Persistence/AppDbContext.cs

@@ -55,16 +55,7 @@ public class AppDbContext : IdentityDbContext<NexusUser>
             entity.HasKey(e => e.ContentHash);
             entity.HasIndex(e => e.ContentHash).IsUnique();
             entity.HasIndex(e => e.TenantId);
-            if (Database.IsNpgsql())
-            {
-                // Configure vector column (768 dims) and HNSW index for cosine similarity
-                entity.Property(e => e.Embedding).HasColumnType("vector(768)");
-                entity.HasIndex(e => e.Embedding).HasMethod("hnsw").HasOperators("vector_cosine_ops");
-            }
-            else
-            {
-                entity.Ignore(e => e.Embedding);
-            }
+            entity.Ignore(e => e.Embedding);
         });
 
         modelBuilder.Entity<KnowledgeUnit>(entity =>

src/NexusReader.Data/Persistence/AppDbContextFactory.cs

@@ -1,7 +1,6 @@
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Design;
 using Microsoft.Extensions.Configuration;
-using Pgvector.EntityFrameworkCore;
 
 namespace NexusReader.Data.Persistence;
 
@@ -38,7 +37,7 @@ public class AppDbContextFactory : IDesignTimeDbContextFactory<AppDbContext>
              connectionString = "Host=localhost;Database=nexus_reader;Username=postgres;Password=postgres";
         }
 
-        optionsBuilder.UseNpgsql(connectionString, x => x.UseVector());
+        optionsBuilder.UseNpgsql(connectionString);
 
         return new AppDbContext(optionsBuilder.Options);
     }