feat(window): expose WindowConfig::app_id() and consume launcher activation tokens - #1085

Problem

Applications built with Floem currently never identify their windows to the
desktop environment:

1. No application name is requested. create_window builds winit's
   WindowAttributes without ever setting a name, so winit never calls
   set_app_id() on Wayland. On X11 the backend silently falls back to
   deriving WM_CLASS from argv[0], masking the issue.

   Result on GNOME Wayland: the window cannot be associated with any
   .desktop entry — taskbars/docks show a generic icon or an "UNKNOWN"
   label, windows don't group, and launch tracking degrades
   (see Lapce is missing icon in a lot of places for Gnome/Wayland lapce#2199).

2. Launcher activation tokens are never consumed. When a desktop shell
   launches an app it passes XDG_ACTIVATION_TOKEN (Wayland) /
   DESKTOP_STARTUP_ID (X11) and keeps the launch in a pending state until
   the token is used. Unconsumed, shells fall back to a timeout (~15s on
   GNOME), during which the dock shows a launching animation instead of the
   app entry.

Protocol capture of an affected app confirms no set_app_id is ever sent:

> WAYLAND_DEBUG=1 lapce |& grep app_id      # before: no output at all

Change

This PR adds two small, opt-in capabilities to window creation:

• WindowConfig::app_id(impl Into<String>) — declares the application
  identity. When set, floem applies it via winit's
  WindowAttributesExtWayland::with_name() / WindowAttributesExtX11::with_name()
  (Wayland app_id, X11 WM_CLASS). When unset, behaviour is exactly as
  before.
• Activation token consumption — if the process was spawned by a desktop
  launcher, the token reported by
  EventLoopExtStartupNotify::read_token_from_env() is attached with
  WindowAttributesExtStartupNotify::with_activation_token(), letting the
  compositor complete the startup sequence immediately.

Both are #[cfg(target_os = "linux")]; other platforms are untouched.

Why lapce-backports

Lapce pins this branch, so this is where the fix can reach the editor's next
release. I'm happy to port it to main as well once this lands or once the
direction is confirmed (main's new window-creation layout needs a slightly
different patch shape due to the winit-core split).

Testing

• Built and run against Lapce on Zorin OS (GNOME, Wayland, 2x scale):
  • Before: dock/taskbar shows "UNKNOWN" / no icon; entry appears only after
    ~15s.
  • After: correct application icon immediately on window map.
• Protocol verification (WAYLAND_DEBUG=1) now shows
  xdg_toplevel.set_app_id("dev.lapce.lapce") before the surface maps.
• No unit tests added: the behaviour is platform integration (compositor +
  shell side). Happy to add builder-level tests if preferred.