refactor: remove assistant chat archiving

packages/db/migrations/postgresql/0010_workable_shard.sql

@@ -24,7 +24,6 @@ CREATE TABLE "assistant_thread" (
 	"user_id" varchar(64) NOT NULL,
 	"title" varchar(256),
 	"model_id" varchar(256),
-	"status" varchar(16) DEFAULT 'regular' NOT NULL,
 	"created_at" timestamp DEFAULT now() NOT NULL,
 	"updated_at" timestamp DEFAULT now() NOT NULL
 );