fix(tabs): preserve runtime channel across Settings Save, deep-clone seeded CurrentChannel

Smoke-test round 4 surfaced a clean reproducer: a Party or Linkshell
tab with channel /p, then Settings → Save, popped the input back to
/tell <pinned-partner> on the next interaction. Two bugs combined:

1. Configuration.UpdateFrom captured only Messages+LastSendUnread from
   the live state during the persistent-tab merge. CurrentChannel was
   not preserved, so a Settings save overwrote the runtime channel
   state with the settings-time snapshot. If the user switched channel
   in-game between Settings-open and Settings-save, that switch was
   lost. Live CurrentChannel now joins Messages and LastSendUnread in
   the per-Identifier preservation tuple.

2. TabSwitched seeded a new tab's CurrentChannel from previousTab via
   reference copy (`newTab.CurrentChannel = previousTab.CurrentChannel`).
   That left both tabs sharing the same UsedChannel instance, so a
   later mutation on one bled into the other — exactly the path that
   carried a pinned tell-target onto Party. Switched to a deep clone
   (UsedChannel.Clone(), same Cherry-Pick-Patch-B pattern from v1.4.6)
   plus a Debug log so the next smoke can confirm at a glance which
   previous tab donated its channel state.

Pre-existing ChatTwo upstream pattern; v1.4.7 just made it visible
because pinned tabs are now the kind of long-lived tell-target that
sticks around for the seed path to grab.

HellionChat/Ui/ChatLogWindow.cs

@@ -441,11 +441,24 @@ public sealed class ChatLogWindow : Window
 
     private void TabSwitched(Tab newTab, Tab previousTab)
     {
-        // Use the fixed channel if set by the user, or set it to the current tabs channel if this tab wasn't accessed before
+        // Use the fixed channel if set by the user. Otherwise, if the new tab
+        // has no channel state yet (fresh from JSON, never selected this
+        // session), seed from the previous tab — but deep-clone so we don't
+        // share TellTarget with the previous tab. Without the clone, a later
+        // /tell on the new tab would mutate the pinned tab's TellTarget and
+        // the Party/Linkshell channel would pop back to the pinned tell-mark.
         if (newTab.Channel is not null)
+        {
             newTab.CurrentChannel.Channel = newTab.Channel.Value;
+        }
         else if (newTab.CurrentChannel.Channel is InputChannel.Invalid)
-            newTab.CurrentChannel = previousTab.CurrentChannel;
+        {
+            newTab.CurrentChannel = previousTab.CurrentChannel.Clone();
+            Plugin.LogProxy.Debug(
+                $"[Tab] '{newTab.Name}' seeded channel from '{previousTab.Name}' "
+                    + $"(Channel={newTab.CurrentChannel.Channel}, TellTarget={newTab.CurrentChannel.TellTarget?.ToTargetString() ?? "null"})"
+            );
+        }
 
         SetChannel(newTab.CurrentChannel.Channel);
     }