feat(qt): Wallpaper follows the window on Plasma Wayland; its blurred twin drifts

"Wallpaper" now behaves like a window that sees straight through to the
desktop: it always paints the part of the wallpaper that lies under the
window, wherever the window is moved, with a stronger blur so nothing in
the picture competes with the text. X11, macOS and Windows already told
Qt where the window is. Wayland does not, so on KDE Plasma a tracker
reads the window's geometry from org_kde_plasma_window_management on its
own client connection and thread (wayland-client + the plasma protocol
crate, pure Rust backend). It follows this process's windows only,
drops every other window's object after its initial state, and
republishes only when the geometry list changes; the field picks the
window by size and ignores updates while another background is showing.
Where the protocol is not offered the crop stays centred and one line is
logged.

KWin hands that protocol only to a binary whose desktop entry names it by
an absolute Exec and lists it in X-KDE-Wayland-Interfaces, so the Linux
desktop entries now carry both (the deb/rpm /usr/bin/qbz symlink resolves
to the same binary). The AppImage step restores the bare Exec name that
linuxdeploy resolves inside the AppDir, and the Nix package rewrites Exec
to its store path.

"Wallpaper, blurred" is Blurred art with the wallpaper in the cover's
place, so it now drifts while the transport plays and holds still when it
does not.

cc

crates/Cargo.lock

@@ -1458,6 +1458,12 @@ dependencies = [
  "litrs",
 ]
 
+[[package]]
+name = "downcast-rs"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "75b325c5dbd37f80359721ad39aca5a29fb04c89279657cffdda8736d0c0b9d2"
+
 [[package]]
 name = "dst-decoder"
 version = "0.1.2"
@@ -4494,6 +4500,8 @@ dependencies = [
  "url",
  "urlencoding",
  "uuid 1.26.0",
+ "wayland-client",
+ "wayland-protocols-plasma",
  "windows-sys 0.61.2",
  "winresource",
  "zbus 5.19.0",
@@ -6812,6 +6820,76 @@ dependencies = [
  "web-sys",
 ]
 
+[[package]]
+name = "wayland-backend"
+version = "0.3.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38a91b4eaddff87b1cd1074985e3713da4af2c49742d1b356b2c01670a67a078"
+dependencies = [
+ "cc",
+ "downcast-rs",
+ "rustix 1.1.4",
+ "smallvec",
+ "wayland-sys",
+]
+
+[[package]]
+name = "wayland-client"
+version = "0.31.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3c36a0f861ad76d0901f2800b46321410d9f73f2ea88aac0650d86c32688073"
+dependencies = [
+ "bitflags 2.13.1",
+ "rustix 1.1.4",
+ "wayland-backend",
+ "wayland-scanner",
+]
+
+[[package]]
+name = "wayland-protocols"
+version = "0.32.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23d0c813de3daa2ed6520af85a3bd49b0e722a3078506899aa9686fea58dc4b6"
+dependencies = [
+ "bitflags 2.13.1",
+ "wayland-backend",
+ "wayland-client",
+ "wayland-scanner",
+]
+
+[[package]]
+name = "wayland-protocols-plasma"
+version = "0.3.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b6d8cf1eb2c1c31ed1f5643c88a6e53538129d4af80030c8cabd1f9fa884d91"
+dependencies = [
+ "bitflags 2.13.1",
+ "wayland-backend",
+ "wayland-client",
+ "wayland-protocols",
+ "wayland-scanner",
+]
+
+[[package]]
+name = "wayland-scanner"
+version = "0.31.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "338e30461b3a2b67d70eb30a6d89f8e0c93a833e07d2ae89085cd070c4a00ac0"
+dependencies = [
+ "proc-macro2",
+ "quick-xml",
+ "quote",
+]
+
+[[package]]
+name = "wayland-sys"
+version = "0.31.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d8eab23fefc9e41f8e841df4a9c707e8a8c4ed26e944ef69297184de2785e3be"
+dependencies = [
+ "pkg-config",
+]
+
 [[package]]
 name = "web-sys"
 version = "0.3.104"