fix: make iOS requests recognized by backend (#159)

Adds simple user-agent to make gonfalon recognize iOS. Later should be
made proper but it should be here until gonfalon update

Later should be similar to this
//    func buildUserAgent(sdkVersion: String) -> String {
//        let device = UIDevice.current
// let osVersion = device.systemVersion.replacingOccurrences(of: ".",
with: "_")
//        let model = device.model // "iPhone" or "iPad"
// let buildNumber = Bundle.main.infoDictionary?["CFBundleVersion"] as?
String ?? "0"
//        
//        if model == "iPad" {
// return "Mozilla/5.0 (\(model); CPU OS \(osVersion) like Mac OS X)
Mobile/\(buildNumber) YourSDK/\(sdkVersion)"
//        } else {
// return "Mozilla/5.0 (\(model); CPU \(model) OS \(osVersion) like Mac
OS X) Mobile/\(buildNumber) YourSDK/\(sdkVersion)"
//        }
//    }


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: adds a static `User-Agent` default header to outgoing
GraphQL requests, with no change to request/response handling beyond the
extra header.
> 
> **Overview**
> Adds a default `User-Agent: iOS` header to `GraphQLClient`’s
`defaultHeaders`, ensuring all GraphQL requests identify as iOS unless
explicitly overridden by per-call headers.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
164b955. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: abelonogov-ld

Sources/Common/GraphQL/GraphQLClient.swift

@@ -13,7 +13,8 @@ public final class GraphQLClient {
                 decoder: JSONDecoder = JSONDecoder(),
                 defaultHeaders: [String: String] = [
                     "Content-Type": "application/json",
-                    "Accept": "application/json"
+                    "Accept": "application/json",
+                    "User-Agent": "iOS"
                 ]) {
         self.endpoint = endpoint
         self.network = network