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

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -1,5 +1,6 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Configuration;
+using Pgvector.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.AI;
 using GeminiDotnet;
@@ -24,13 +25,13 @@ public static class DependencyInjection
         var pgConnectionString = configuration.GetConnectionString("PostgresConnection");
         if (!string.IsNullOrEmpty(pgConnectionString))
         {
-            services.AddDbContext<AppDbContext>(options =>
-                options.UseNpgsql(pgConnectionString));
+            services.AddDbContextFactory<AppDbContext>(options =>
+                options.UseNpgsql(pgConnectionString, x => x.UseVector()));
         }
         else
         {
             var sqliteConnectionString = configuration.GetConnectionString("SqliteConnection") ?? "Data Source=nexus.db";
-            services.AddDbContext<AppDbContext>(options =>
+            services.AddDbContextFactory<AppDbContext>(options =>
                 options.UseSqlite(sqliteConnectionString));
         }
 
@@ -64,6 +65,12 @@ public static class DependencyInjection
             ModelId = aiSettings.Model 
         }));
 
+        services.AddEmbeddingGenerator(new GeminiEmbeddingGenerator(new GeminiClientOptions
+        {
+            ApiKey = aiSettings.ApiKey,
+            ModelId = aiSettings.EmbeddingModel ?? "text-embedding-004"
+        }));
+
         services.AddScoped<IKnowledgeService, KnowledgeService>();
         services.AddTransient<IEpubService, EpubService>();