Move Custom Battle to lobby with OAuth authentication (#5051)

* Move Custom Battle to lobby, use OAuth authentication

- Remove _createConnection() from _internalCustomBattle() since connection
  already exists when called from lobby
- Hide gameSelectionPanel instead of connectionPanel when entering custom battle
- Add customBattleButton field for lobby UI button
- Add cancelCustomBattleButton and CancelCustomBattle() to return to lobby
- Wire up button click handlers in SetupLobbyUI()

The Custom Battle button should now be placed in the gameSelectionPanel (lobby)
in Unity and assigned to the customBattleButton field. A cancel button in the
customBattlePanel should be assigned to cancelCustomBattleButton.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Wire up Custom Battle and Cancel buttons in Unity scene

- Assign customBattleButton in lobby panel
- Assign cancelCustomBattleButton in custom battle panel

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Fix CancelCustomBattle to properly reset canvas states

Hide shardokCanvas and ensure connectionCanvas is visible when
returning to lobby from custom battle.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Fix Back button onClick handler in custom battle panel

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

src/main/csharp/net/eagle0/clients/unity/eagle0/Assets/ConnectionHandler/ConnectionHandler.cs

@@ -112,6 +112,8 @@ public class ConnectionHandler : MonoBehaviour, ILobbySubscriber, IDisposable {
 
     [Header("Lobby Controls")]
     public Button logoutButton;
+    public Button customBattleButton;
+    public Button cancelCustomBattleButton;
     public TextMeshProUGUI lobbyEnvironmentText;
     public TextMeshProUGUI lobbyUserText;
 
@@ -276,6 +278,10 @@ public class ConnectionHandler : MonoBehaviour, ILobbySubscriber, IDisposable {
 
     private void SetupLobbyUI() {
         if (logoutButton != null) { logoutButton.onClick.AddListener(OnLogoutClicked); }
+        if (customBattleButton != null) { customBattleButton.onClick.AddListener(CustomBattle); }
+        if (cancelCustomBattleButton != null) {
+            cancelCustomBattleButton.onClick.AddListener(CancelCustomBattle);
+        }
     }
 
     private void UpdateLobbyStatusDisplays() {
@@ -501,6 +507,14 @@ public class ConnectionHandler : MonoBehaviour, ILobbySubscriber, IDisposable {
 
     public void CustomBattle() { _internalCustomBattle(); }
 
+    public void CancelCustomBattle() {
+        customBattlePanel.SetActive(false);
+        shardokCanvas.gameObject.SetActive(false);
+        connectionCanvas.gameObject.SetActive(true);
+        gameSelectionPanel.SetActive(true);
+        StartListeningForLobbyUpdates();
+    }
+
     public void OnApplicationQuit() { Dispose(); }
 
     public void Dispose() {
@@ -666,12 +680,12 @@ public class ConnectionHandler : MonoBehaviour, ILobbySubscriber, IDisposable {
     }
 
     private void _internalCustomBattle() {
-        _createConnection();
+        // Connection already exists when called from lobby
         _persistentClientConnection.SetLobbySubscriber(this);
 
         SetCustomBattleActive(true);
 
-        connectionPanel.SetActive(false);
+        gameSelectionPanel.SetActive(false);
         customBattlePanel.SetActive(true);
     }