Code-based authorization for Drop clients (#145)

* feat: code-based authorization

* fix: final touches

* fix: require session on code fetch endpoint

* feat: better error handling

* refactor: move auth send to client handler

* fix: lint

server/internal/tasks/index.ts

@@ -445,6 +445,7 @@ export type TaskMessage = {
 
 export type PeerImpl = {
   send: (message: string) => void;
+  close: () => void;
 };
 
 export interface BuildTask {