Web SDK: CAN_NOT_GET_GATEWAY_SERVER: invalid vendor key, can not find appid - same App ID works on native platforms (macOS, iOS, Android)

### Version of the agora_rtc_engine

When using agora_rtc_engine: 6.5.3 on Flutter Web with iris-web-rtc_n450_w4220_0.8.6.js, joining a channel fails with the following error even though the exact same App ID works correctly on macOS, iOS, and Android:

[Iris error]: data: {"retry":false,"desc":["invalid vendor key, can not find appid"]}
AgoraRTCException: flag: 4096, message: AgoraRTCError CAN_NOT_GET_GATEWAY_SERVER: invalid vendor key, can not find appid

This results in ErrorCodeType.errJoinChannelRejected being fired in the onError event handler

Environment:

agora_rtc_engine: 6.5.3
iris-web-rtc: n450_w4220_0.8.6
Flutter: 3.38.10
Browser: Chrome
Platform: macOS (host), running Flutter Web on localhost

Link to my own testing project:
https://github.com/sb-dor/agorawebrtc

### Platforms affected

- [ ] Android
- [ ] iOS
- [ ] macOS
- [ ] Windows
- [x] Web

### Steps to reproduce

Create a Flutter project with agora_rtc_engine: ^6.5.3
Add iris-web-rtc_n450_w4220_0.8.6.js to web/index.html as documented
Run on Chrome (flutter run -d chrome --web-hostname localhost --web-port 8080 --dart-define-from-file=config/production.json)
Attempt to join a channel using a valid App ID
Error is thrown — same App ID joins successfully on macOS/iOS/Android

### Expected results

Joining a channel on Flutter Web should succeed with the same App ID that works on native platforms (macOS, iOS, Android). The onJoinChannelSuccess callback should fire and the call should connect.

### Actual results

The join fails immediately with:

[Iris error]: data: {"retry":false,"desc":["invalid vendor key, can not find appid"]}
AgoraRTCException: flag: 4096, message: AgoraRTCError CAN_NOT_GET_GATEWAY_SERVER: invalid vendor key, can not find appid
onError fires with ErrorCodeType.errJoinChannelRejected. The same App ID joins successfully on macOS, iOS, and Android without any changes to the code or configuration.

### Logs

Logs

```console
[10:23:53:099][Iris error]:data: {"retry":false,"csIp":"128.1.77.34","desc":["invalid vendor key, can not find appid"]}
AgoraRTCException: flag: 4096, message: AgoraRTCError CAN_NOT_GET_GATEWAY_SERVER: invalid vendor key, can not find appid
at Tk (http://localhost:8080/iris-web-rtc_n450_w4220_0.8.6.js:2:19373)
at e.gatewayInfo.rm.joinChooseServer.lts (http://localhost:8080/iris-web-rtc_n450_w4220_0.8.6.js:2:16925)
at async http://localhost:8080/iris-web-rtc_n450_w4220_0.8.6.js:1:184043
2
rrror ErrorCodeType.errJoinChannelRejected
10:23 | Controller | CallController | Errororor: ErrorCodeType.errJoinChannelRejected
10:23 | Errororor: ErrorCodeType.errJoinChannelRejected
```

### Flutter Doctor output

Doctor output

```console
[!] Flutter (Channel [user-branch], 3.38.10, on macOS 15.7 24G222 darwin-arm64, locale ru-TJ)
! Flutter version 3.38.10 on channel [user-branch] at /Users/avaz/development/flutter
Currently on an unknown channel. Run `flutter channel` to switch to an official channel.
If that doesn't fix the issue, reinstall Flutter by following instructions at https://flutter.dev/setup.
! Upstream repository unknown source is not a standard remote.
Set environment variable "FLUTTER_GIT_URL" to unknown source to dismiss this error.
[✓] Android toolchain - develop for Android devices (Android SDK version 36.1.0-rc1)
[✓] Xcode - develop for iOS and macOS (Xcode 16.4)
[✓] Chrome - develop for the web
[✓] Connected device (2 available)
[✓] Network resources
```