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/handlers/xdg_shell.rs

@@ -254,7 +254,7 @@ impl XdgShellHandler for Ferese {
     }
 
     fn grab(&mut self, surface: PopupSurface, seat: wl_seat::WlSeat, serial: Serial) {
-        if self.session_lock.active {
+        if self.session_lock.active || self.input_capture.active() {
             return;
         }
         let Some(seat) = Seat::from_resource(&seat) else {