fix(tell): couple CurrentTab to the active tab, retire LastTab

Plugin.CurrentTab now delegates to MainWindow.ActiveTab (fallback Tabs[0]) instead of the never-assigned LastTab index, so the game hooks, unread tracking, notification sounds, InputDisabled and Foray/Eureka paths all operate on the tab the user actually has selected. The dead LastTab/WantedTab fields and both WantedTab writes are removed.

A reference-based MainWindow.ResetActiveTabIfRemoved repairs the active-tab reference on eviction/logout (immune to the SaveConfig temp-tab strip window). The worker-thread eviction path marshals it onto the framework thread so the strip mutation serializes with Draw; logout is already framework-thread. The Draw-seed gains a lazy re-seed for a wholesale config swap. Adds CurrentTabCouplingStep (headless) and the interactive CurrentTabGuidedStep self-test (step count 30 -> 32).

HellionChat/Ui/Windows/MainWindow.cs

@@ -119,6 +119,22 @@ internal sealed class MainWindow : Window
 
     public Tab? ActiveTab => _activeTab;
 
+    // Re-anchors the active-tab reference when the tab it points at is removed
+    // (eviction / logout). Reference compare, so it is immune to the SaveConfig
+    // temp-tab strip window where a tab is briefly absent from Config.Tabs; the
+    // re-seeded tab runs through OnTabActivated so a programmatic switch strips
+    // stale tell state the way a click would.
+    internal void ResetActiveTabIfRemoved(Tab removed)
+    {
+        if (!ReferenceEquals(_activeTab, removed))
+            return;
+
+        var next = Plugin.Config.Tabs.Count > 0 ? Plugin.Config.Tabs[0] : null;
+        _activeTab = next;
+        if (next is not null)
+            TabLifecycleHelpers.OnTabActivated(next, removed);
+    }
+
     // Internal accessors for self-tests so the probes can reach the live
     // component without exposing them as public surface.
     internal Components.Sidebar GetSidebarForSelfTest() => _sidebar;
@@ -163,6 +179,18 @@ internal sealed class MainWindow : Window
             // (pre-coupling the detour wrote here); strip it like any activation.
             TabLifecycleHelpers.OnTabActivated(seeded, null);
         }
+        else if (_activeTab is { } active && !Plugin.Config.Tabs.Contains(active))
+        {
+            // Active tab is no longer in the list (e.g. a wholesale config import
+            // the service repair paths never see). Re-seed on the Draw thread. The
+            // Contains read shares the pre-existing unsynchronized-Tabs-list
+            // exposure that spec §6 defers (SaveConfig also strips from the worker
+            // thread); this adds one more racing read, not a new hazard class.
+            var reseed = Plugin.Config.Tabs.Count > 0 ? Plugin.Config.Tabs[0] : null;
+            _activeTab = reseed;
+            if (reseed is not null)
+                TabLifecycleHelpers.OnTabActivated(reseed, active);
+        }
 
         var statusHeight = Components.StatusBar.Height;