feat: full desktop passthrough with dynamic cursor hole

Replace static input region with a dynamically updated wl_region that
follows the cursor. The full screen receives pointer events except for a
512px hole around the cursor position, allowing clicks and scrolls to
pass through to the desktop. Cursor avoidance shader updates in sync.

Cargo.toml

@@ -9,6 +9,7 @@ rust-version = "1.85"
 [dependencies]
 anyhow = "1.0"
 bytemuck = { version = "1", features = ["derive"] }
+niri-ipc = "25.11.0"
 nix = { version = "0.29", features = ["signal", "process", "poll"] }
 pollster = "0.4"
 raw-window-handle = "0.6"