launcher: pass PhotonCloudRegion to patcher template

DorkNet.ClientMod's config reads PhotonCloudRegion alongside the
AppIds, and the joining client needs the host's region to connect
to the right Photon cloud. Adds {PHOTON_REGION} to the substitution
map and threads region through ClientPatcher.ApplyAsync from both
host (AppState.PhotonRegion) and join (JoinPayload.PhotonRegion)
flows.

launcher/Backend/ClientPatcher.cs

@@ -28,7 +28,8 @@ namespace DorkNet.Launcher.Backend;
 /// }
 /// </code>
 /// Config template placeholders: <c>{HOST}</c>, <c>{PHOTON_APPID}</c>,
-/// <c>{PHOTON_VOICE_APPID}</c>. Anything else passes through unchanged.</para></summary>
+/// <c>{PHOTON_VOICE_APPID}</c>, <c>{PHOTON_REGION}</c>. Anything else
+/// passes through unchanged.</para></summary>
 public sealed class ClientPatcher
 {
     private const string DefaultPluginDest = "MelonLoader/Mods";
@@ -39,11 +40,12 @@ public sealed class ClientPatcher
         string recRoomDataPath,
         string photonAppId,
         string photonVoiceAppId,
+        string photonRegion,
         string apexHost,
         CancellationToken ct = default)
     {
         return Task.Run(() => ApplyCore(patcherDir, recRoomDataPath,
-            photonAppId, photonVoiceAppId, apexHost), ct);
+            photonAppId, photonVoiceAppId, photonRegion, apexHost), ct);
     }
 
     private PatchResult ApplyCore(
@@ -51,6 +53,7 @@ public sealed class ClientPatcher
         string recRoomDataPath,
         string photonAppId,
         string photonVoiceAppId,
+        string photonRegion,
         string apexHost)
     {
         var log = new System.Text.StringBuilder();
@@ -133,7 +136,8 @@ public sealed class ClientPatcher
                     .Replace("{HOST}", apexHost ?? "")
                     .Replace("{PHOTON_APPID}", photonAppId ?? "")
                     .Replace("{PHOTON_VOICE_APPID}",
-                        string.IsNullOrEmpty(photonVoiceAppId) ? photonAppId ?? "" : photonVoiceAppId);
+                        string.IsNullOrEmpty(photonVoiceAppId) ? photonAppId ?? "" : photonVoiceAppId)
+                    .Replace("{PHOTON_REGION}", string.IsNullOrEmpty(photonRegion) ? "us" : photonRegion);
                 File.WriteAllText(configDest, rendered);
                 log.AppendLine($"[patch] wrote config: {Path.GetFileName(configDest)}");
             }

launcher/MainWindow.xaml.cs

@@ -224,7 +224,7 @@ public partial class MainWindow : Window
             HostStatusText.Text = "Patching your Rec Room client…";
             var patch = await _patcher.ApplyAsync(
                 patcherDir, _state.RecRoomPath!,
-                _state.PhotonAppId, _state.PhotonVoiceAppId, _hostApex);
+                _state.PhotonAppId, _state.PhotonVoiceAppId, _state.PhotonRegion, _hostApex);
             if (!patch.Ok) { ShowError("Patcher failed: " + Truncate(patch.Log, 500)); return; }
 
             var code = JoinCode.Encode(new JoinPayload
@@ -324,7 +324,7 @@ public partial class MainWindow : Window
             JoinStatusText.Text = "Patching your Rec Room client…";
             var patch = await _patcher.ApplyAsync(
                 patcherDir, _state.RecRoomPath!,
-                payload.PhotonAppId, payload.PhotonVoiceAppId, payload.Host);
+                payload.PhotonAppId, payload.PhotonVoiceAppId, payload.PhotonRegion, payload.Host);
             if (!patch.Ok) { ShowError("Patcher failed: " + Truncate(patch.Log, 500)); return; }
 
             JoinStatusText.Text = $"Patched and ready. Connecting to {payload.Host}. " +

launcher/RELEASES.md

@@ -95,6 +95,7 @@ Defaults:
 | `{HOST}` | Host's tunnel hostname (or join code's `host` field) |
 | `{PHOTON_APPID}` | Host's Photon Realtime AppId |
 | `{PHOTON_VOICE_APPID}` | Host's Photon Voice AppId (falls back to Realtime if empty) |
+| `{PHOTON_REGION}` | Photon Cloud region (us/eu/asia/jp/sa/kr/in/au); defaults to `us` |
 
 Example template: