Implement native InputCapture with private EIS receiver transport

Add consent, zones and outside-edge barriers, connection-scoped leases, bounded input queues and keyboard/pointer forwarding. Restore local input on release, locking, topology or keymap changes, receiver loss and emergency escape. Preserve held-key state and distinguish finger stops from absent scroll axes.

Validation: independent review cleared; 5 native InputCapture unit tests; 32 portal tests; official D-Bus contract checks on a private bus; real installed libei receiver interoperability test. Live physical barrier and consent interaction remain to be checked in a desktop session.

compositor/src/winit.rs

@@ -2863,6 +2863,9 @@ fn cursor_elements(
     output_geometry: Rectangle<i32, Logical>,
     scale: f64,
 ) -> Vec<AnimatedWindowRenderElement> {
+    if state.input_capture.active() {
+        return Vec::new();
+    }
     let Some(pointer) = state.seat.get_pointer() else {
         return Vec::new();
     };