feat: add kde wayland support

[Merrit]

On KDE Plasma + Wayland, window management is no longer possible through
X11 tools (xdotool, wmctrl). This commit introduces a KDE-specific backend
that uses KWin scripting and D-Bus to provide the same suspend/resume
functionality on that platform.

How it works:

• At startup on a KDE Wayland session, two KWin scripts are loaded via the
  KWin D-Bus API (org.kde.KWin). list_windows_kde.js enumerates all open
  windows and pushes them to Nyrna over D-Bus. active_window_kde.js sets
  up a persistent workspace.windowActivated listener that sends every
  subsequent focus change to Nyrna in real time.
• Nyrna registers its own session D-Bus service (codes.merritt.Nyrna) via a
  generated NyrnaDbus object. The two KWin scripts call methods on this
  service (updateWindows, updateActiveWindow) to deliver their data.
• Window minimize/restore on KDE Wayland is handled by writing a transient
  KWin script to disk and loading it each time it is needed, because the KWin
  scripting API does not expose a direct minimize/restore D-Bus call.

Architecture changes:

• NativePlatform() is replaced by an async NativePlatform.initialize()
  factory. The extra async step is needed on Linux to resolve the session
  type, set up D-Bus, and (on KDE Wayland) load the KWin scripts before the
  rest of the app starts.
• activeWindow() (async method) is replaced by an activeWindow mutable
  field updated by checkActiveWindow(). On KDE Wayland the field is kept
  current by the persistent D-Bus subscription, so checkActiveWindow() only
  needs to wait (poll up to 2 s) for the initial value.
• A new SessionType value type combines DisplayProtocol (wayland / x11 /
  unknown) with DesktopEnvironment (kde / gnome / xfce / unknown). It is
  populated once during Linux.initialize() and exposed as a synchronous
  getter, removing the need for async session-type checks later.
• ActiveWindowService selects the X11 or Wayland code path based on
  SessionType. ActiveWindowX11 and ActiveWindowWayland hold the
  platform-specific logic.
• Window IDs are now String instead of int to accommodate KDE Wayland's
  UUID-style internalId values. X11 integer IDs are stringified.
• NativePlatform.dispose() tears down D-Bus connections and cancels KWin
  script subscriptions. AppCubit.close() and the toggle-mode code path in
  main() both call it.

Wayland support can be extended in the future for other DEs, using the shared infrastructure introduced here.