fix(closeout): address closure-review findings

- gate keybind pill-sync on IsChannelOrExistingLinkshell so an empty
  linkshell slot no longer desyncs the pill from the real send channel
- close manually-popped pop-out windows on logout via an IsOpen filter
  instead of the PopOut flag (which manual pops never set)
- read the router's tell-tab lookup through a lock-wrapped accessor so the
  framework thread cannot enumerate Config.Tabs mid worker-thread mutation
- add a "switch on every tell" toggle (default on) and make the auto-open
  mode pick the matching layout, so Sidebar vs Top-tab are distinct
- comment corrections (stale/contradictory text, TEST-MIRROR path depth)

HellionChat/Ui/Windows/MainWindow.cs

@@ -161,8 +161,8 @@ internal sealed class MainWindow : Window
     }
 
     // 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).
+    // no-op; a null active tab seeds the index to 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.