feat(window): restore hide-chat-window + Enter-to-restore (1.5.6)

The eye/hide button now hides the HellionChat window (runtime-only, via a new
DrawConditions gate) instead of toggling native-chat suppression, matching 1.5.6.
The chat-activation keybind (Enter / "/"), whose dispatch was a dead stub in the
KeybindManager since the v1.6.0 rewrite, is re-wired to MainWindow.ActivateChat:
it un-hides, opens if closed, brings the window to front and focuses the input --
so the chat reacts to Enter again from any state. /hellion is a reliable one-press
recovery (Toggle now clears the hide), and the window always shows on login
(start state no longer read from the persisted flag). Adds HideRestoreSelfTestStep.

HellionChat/Ui/Windows/MainWindow.cs

@@ -33,6 +33,10 @@ internal sealed class MainWindow : Window
 
     private Tab? _activeTab;
 
+    // Runtime-only hide: window stays IsOpen but DrawConditions skips it, so the
+    // chat-activation key can restore it (1.5.6 HideState.User parity).
+    private bool _userHidden;
+
     public Vector2 LastWindowPos { get; private set; } = Vector2.Zero;
     public Vector2 LastWindowSize { get; private set; } = Vector2.Zero;
     internal unsafe ImGuiViewport* LastViewport;
@@ -66,7 +70,9 @@ internal sealed class MainWindow : Window
             MinimumSize = new Vector2(MinWidth, MinHeight),
             MaximumSize = new Vector2(float.MaxValue, float.MaxValue),
         };
-        IsOpen = Plugin.Config.MainWindowOpen;
+        // 1.5.6 parity: the chat always shows on login. The window stays closeable
+        // and hideable within a session, but that state is not carried across starts.
+        IsOpen = true;
         RespectCloseHotkey = false;
     }
 
@@ -162,11 +168,33 @@ internal sealed class MainWindow : Window
 
     internal Components.MessageList GetMessageListForSelfTest() => _messages;
 
-    // new-shadow on Window.Toggle so the open path also writes Config —
-    // OnClose already covers the close path through the base behaviour.
+    public override bool DrawConditions() => !_userHidden;
+
+    internal void UserHide() => _userHidden = true;
+
+    // Chat-activation keybind (Enter) entry point. Field writes only, so it is safe
+    // from the framework thread; the draw path applies focus next frame.
+    internal void ActivateChat()
+    {
+        _userHidden = false;
+        if (!IsOpen)
+        {
+            IsOpen = true;
+            Plugin.Config.MainWindowOpen = true;
+        }
+        BringToFront();
+        _input.Activate = true;
+    }
+
+    // new-shadow on Window.Toggle so the open path also writes Config. A user-hide
+    // counts as "not visible", so /hellion is a reliable one-press recovery even when
+    // the Enter keybind can't fire (DirectChat / a focused game text field).
     public new void Toggle()
     {
-        IsOpen = !IsOpen;
+        var visible = IsOpen && !_userHidden;
+        IsOpen = !visible;
+        if (IsOpen)
+            _userHidden = false;
         Plugin.Config.MainWindowOpen = IsOpen;
     }