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/tree.rs

@@ -0,0 +1,57 @@
+#![cfg_attr(target_family = "wasm", no_main)]
+//! Renders a div with deep children hierarchy. This example is useful to exemplify that Zed can
+//! handle deep hierarchies (even though it cannot just yet!).
+use std::sync::LazyLock;
+
+use gpui::{App, Bounds, Context, Window, WindowBounds, WindowOptions, div, prelude::*, px, size};
+use gpui_platform::application;
+
+struct Tree {}
+
+static DEPTH: LazyLock<u64> = LazyLock::new(|| {
+    std::env::var("GPUI_TREE_DEPTH")
+        .ok()
+        .and_then(|depth| depth.parse().ok())
+        .unwrap_or_else(|| 50)
+});
+
+impl Render for Tree {
+    fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
+        let mut depth = *DEPTH;
+        static COLORS: [gpui::Hsla; 4] = [gpui::red(), gpui::blue(), gpui::green(), gpui::yellow()];
+        let mut colors = COLORS.iter().cycle().copied();
+        let mut next_div = || div().p_0p5().bg(colors.next().unwrap());
+        let mut innermost_node = next_div();
+        while depth > 0 {
+            innermost_node = next_div().child(innermost_node);
+            depth -= 1;
+        }
+        innermost_node
+    }
+}
+
+fn run_example() {
+    application().run(|cx: &mut App| {
+        let bounds = Bounds::centered(None, size(px(300.0), px(300.0)), cx);
+        cx.open_window(
+            WindowOptions {
+                window_bounds: Some(WindowBounds::Windowed(bounds)),
+                ..Default::default()
+            },
+            |_, cx| cx.new(|_| Tree {}),
+        )
+        .unwrap();
+    });
+}
+
+#[cfg(not(target_family = "wasm"))]
+fn main() {
+    run_example();
+}
+
+#[cfg(target_family = "wasm")]
+#[wasm_bindgen::prelude::wasm_bindgen(start)]
+pub fn start() {
+    gpui_platform::web_init();
+    run_example();
+}