feat(keybind): cycle tabs and switch channel with pill sync

HellionChat/Ui/Windows/MainWindow.cs

@@ -160,6 +160,25 @@ internal sealed class MainWindow : Window
         TabLifecycleHelpers.OnTabActivated(tab, previous);
     }
 
+    // Tab-cycle entry point for the ChatTabForward/Backward keybinds. Empty list is a
+    // no-op; a null active tab seeds tabs[0]; a single-tab cycle that lands on the
+    // already-active tab is a no-op (ActivateTab early-returns on the same reference).
+    // Routes through ActivateTab so the cycle strips stale tell state + re-derives the
+    // channel exactly like a sidebar/top-tab click. Pop-out focus-forward stays
+    // deferred (no focus contract) — main-window tabs only.
+    internal void ChangeTabDelta(int delta)
+    {
+        var tabs = Plugin.Config.Tabs;
+        if (tabs.Count == 0)
+            return;
+
+        var idx = _activeTab is null ? 0 : tabs.IndexOf(_activeTab);
+        if (idx < 0)
+            idx = 0; // active tab not in the list (mid-strip) -> start from the first
+
+        ActivateTab(tabs[TabLifecycleHelpers.WrapTabIndex(idx, delta, tabs.Count)]);
+    }
+
     // Internal accessors for self-tests so the probes can reach the live
     // component without exposing them as public surface.
     internal Components.Sidebar GetSidebarForSelfTest() => _sidebar;