Make vertical tab close (×) buttons reliably hittable

Two issues kept the close button unusable:
- The launcher-row close button lacked flex_shrink_0, so on narrow
  sidebars the title swallowed the 16 px hit target before flex laid
  it out.
- The handler did select_tab(close_id) → close_active_tab(); if the
  newly-selected tab routed through split-view close logic the call
  silently no-op'd against the user's intent.

Add flex_shrink_0 on both launcher and tab close buttons, and route
the click through a new close_tab_by_id helper that calls
BrowserCore::close_tab(tab_id) directly.

crates/ely_app/src/shell/tab_lifecycle.rs

@@ -33,4 +33,24 @@ impl ElyShell {
             cx.notify();
         }
     }
+
+    /// Close a specific tab by id. Used by the per-row close (×) on
+    /// vertical tabs and launcher rows: closing the tab the user
+    /// targeted directly, instead of the prior select-then-close
+    /// dance which depended on `close_active_tab` doing the right
+    /// thing after a fresh selection (and which silently no-op'd if
+    /// the active tab routed into split-view close logic).
+    pub(super) fn close_tab_by_id(
+        &mut self,
+        tab_id: &TabId,
+        window: &mut Window,
+        cx: &mut Context<Self>,
+    ) {
+        if let ShellState::Ready(core) = &mut self.state
+            && core.close_tab(tab_id).is_ok()
+        {
+            self.sync_address_input(window, cx);
+            cx.notify();
+        }
+    }
 }