Add Swagger docs at /docs and /openapi.json; frontend and backend updates

Made-with: Cursor

backend/src/middleware/nip98.ts

@@ -93,6 +93,7 @@ export async function nip98Auth(req: Request, res: Response, next: NextFunction)
     res.status(401).json({
       code: "invalid_nip98",
       message: "NIP-98 'u' tag does not match request URL.",
+      details: `signed=${u} server=${absoluteUrl}`,
     });
     return;
   }