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/docs/contexts.md

@@ -0,0 +1,33 @@
+# Contexts
+
+GPUI makes extensive use of _context parameters_ (typically named `cx`) to provide access to application state and services. These contexts are references passed to functions, enabling interaction with global state, windows, entities, and system services.
+
+---
+
+## `App`
+
+The root context granting access to the application's global state. This context owns all entities' data and can be used to read or update the data referenced by an `Entity<T>`.
+
+## `Context<T>`
+
+A context provided when interacting with an `Entity<T>`, with additional methods related to that specific entity such as notifying observers and emitting events. This context dereferences into `App`, meaning any function which can take an `App` reference can also take a `Context<T>` reference, allowing you to access the application's global state.
+
+## `AsyncApp` and `AsyncWindowContext`
+
+Whereas the above contexts are always passed to your code as references, you can call `to_async` on the reference to create an async context, which has a static lifetime and can be held across `await` points in async code. When you interact with entities with an async context, the calls become fallible, because the context may outlive the window or even the app itself.
+
+## `TestAppContext`
+
+These are similar to the async contexts above, but they panic if you attempt to access a non-existent app or window, and they also contain other features specific to tests.
+
+---
+
+# Non-Context Core Types
+
+## `Window`
+
+Provides access to the state of an application window. This type has a root view (an `Entity` implementing `Render`) which it can read/update, but since it is not a context, you must pass a `&mut App` (or a context which dereferences to it) to do so, along with other functions interacting with global state. You can obtain a `Window` from an `WindowHandle` by calling `WindowHandle::update`.
+
+## `Entity<T>`
+
+A handle to a structure requiring state. This data is owned by the `App` and can be accessed and modified via references to contexts. If `T` implements `Render`, then the entity is sometimes referred to as a view. Entities can be observed by other entities and windows, allowing a closure to be called when `notify` is called on the entity's `Context`.