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/gpui/examples/active_state_bug.rs

@@ -0,0 +1,47 @@
+/// Click the button — the `.active()` background gets stuck on every other click.
+use gpui::*;
+use gpui_platform::application;
+
+struct Example;
+
+impl Render for Example {
+    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
+        // Colors from Zed's default dark theme
+        let bg = hsla(215. / 360., 0.12, 0.15, 1.);
+        let text = hsla(221. / 360., 0.11, 0.86, 1.);
+        let hover = hsla(225. / 360., 0.118, 0.267, 1.);
+        let active = hsla(220. / 360., 0.118, 0.20, 1.);
+
+        div().bg(bg).size_full().p_1().child(
+            div()
+                .id("button")
+                .px_2()
+                .py_0p5()
+                .rounded_md()
+                .text_sm()
+                .text_color(text)
+                .hover(|s| s.bg(hover))
+                .active(|s| s.bg(active))
+                .on_click(|_, _, _| {})
+                .child("Click me"),
+        )
+    }
+}
+
+fn main() {
+    application().run(|cx: &mut App| {
+        cx.open_window(
+            WindowOptions {
+                window_bounds: Some(WindowBounds::Windowed(Bounds::centered(
+                    None,
+                    size(px(200.), px(60.)),
+                    cx,
+                ))),
+                ..Default::default()
+            },
+            |_, cx| cx.new(|_| Example),
+        )
+        .unwrap();
+        cx.activate(true);
+    });
+}