refactor: change backend to typescript and update types and variables accordingly

backend/misc/express.d.ts

@@ -0,0 +1,11 @@
+import type {AuthTokenPayload} from "../services/tokenService.js";
+
+declare global {
+    namespace Express {
+        interface Request {
+            user?: AuthTokenPayload;
+        }
+    }
+}
+
+export {};

backend/misc/types.ts

@@ -0,0 +1,8 @@
+export type ErrorCode = readonly [code: string, message: string];
+
+export interface Response {
+    success: boolean;
+    code: string;
+    data: any;
+    message: string;
+}