feat: enforce tenant isolation and shared question bank

Tiku.Worker/Program.cs

@@ -1,6 +1,17 @@
+using Tiku.Application;
+using Tiku.Application.Tenancy;
+using Tiku.Infrastructure;
 using Tiku.Worker;
 
 var builder = Host.CreateApplicationBuilder(args);
+var connectionString = builder.Configuration.GetConnectionString("Database")
+    ?? builder.Configuration["DATABASE_URL"]
+    ?? throw new InvalidOperationException(
+        "Database connection is required. Configure ConnectionStrings:Database or DATABASE_URL.");
+builder.Services.AddApplication();
+builder.Services.AddInfrastructure(connectionString);
+builder.Services.AddOptions<DomainLifecycleOptions>()
+    .Bind(builder.Configuration.GetSection("TenantDomains"));
 builder.Services.AddHostedService<Worker>();
 
 var host = builder.Build();