logiguard fork: GPUI xdg-activation keyboard-focus serial fix

Single-commit orphan branch: full zed-industries/zed @ 8c74db0 source tree
with a 3-file patch applied (no upstream history).

Patch (crates/gpui_linux/src/linux/wayland/):
  - serial.rs: add SerialKind::KeyboardEnter
  - client.rs: store wl_keyboard.enter serial; add latest_serial_of()
  - window.rs: activate() uses keyboard-enter serial (Mutter focus gate)

Mutter honors window activation only when the token carries the keyboard-
focus serial from wl_keyboard.enter; GPUI used a stale mouse-press serial.
See docs/tray-window-focus-wayland.md in logiguard.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/panel/src/panel.rs

@@ -0,0 +1,35 @@
+use gpui::actions;
+use ui::prelude::*;
+
+actions!(
+    panel,
+    [
+        /// Navigates to the next tab in the panel.
+        NextPanelTab,
+        /// Navigates to the previous tab in the panel.
+        PreviousPanelTab
+    ]
+);
+
+pub trait PanelHeader: workspace::Panel {}
+
+/// Implement this trait to enable a panel to have tabs.
+pub trait PanelTabs: PanelHeader {
+    /// Returns the index of the currently selected tab.
+    fn selected_tab(&self, cx: &mut App) -> usize;
+    /// Selects the tab at the given index.
+    fn select_tab(&self, cx: &mut App, index: usize);
+    /// Moves to the next tab.
+    fn next_tab(&self, _: NextPanelTab, cx: &mut App) -> Self;
+    /// Moves to the previous tab.
+    fn previous_tab(&self, _: PreviousPanelTab, cx: &mut App) -> Self;
+}
+
+#[derive(IntoElement)]
+pub struct PanelTab {}
+
+impl RenderOnce for PanelTab {
+    fn render(self, _window: &mut Window, _cx: &mut App) -> impl IntoElement {
+        div()
+    }
+}