refactor: revert unrelated USB gadget type changes

Remove int→int16 type signature changes from internal/usbgadget/ that were
not essential to multi-session functionality. These changes should be part
of a separate USB improvement PR.

Changes:
- Revert AbsMouseReport signature to use int instead of int16
- Remove int16 casts in hidrpc.go calling code
- Update usb.go wrapper functions to match

This keeps the multi-session PR focused on session management without
coupling unrelated USB gadget refactoring.

hidrpc.go

@@ -69,7 +69,7 @@ func handleHidRPCMessage(message hidrpc.Message, session *Session) {
 			logger.Warn().Err(err).Msg("failed to get pointer report")
 			return
 		}
-		rpcErr = rpcAbsMouseReport(int16(pointerReport.X), int16(pointerReport.Y), pointerReport.Button)
+		rpcErr = rpcAbsMouseReport(pointerReport.X, pointerReport.Y, pointerReport.Button)
 	case hidrpc.TypeMouseReport:
 		if !session.HasPermission(PermissionMouseInput) {
 			logger.Debug().

internal/usbgadget/hid_keyboard.go

@@ -354,7 +354,7 @@ func (u *UsbGadget) UpdateKeysDown(modifier byte, keys []byte) KeysDownState {
 	u.keyboardStateLock.Unlock()
 
 	if u.onKeysDownChange != nil {
-		(*u.onKeysDownChange)(state)
+		(*u.onKeysDownChange)(state) // this enques to the outgoing hidrpc queue via usb.go → currentSession.enqueueKeysDownState(...)
 	}
 	return state
 }

internal/usbgadget/hid_mouse_absolute.go

@@ -85,7 +85,7 @@ func (u *UsbGadget) absMouseWriteHidFile(data []byte) error {
 	return nil
 }
 
-func (u *UsbGadget) AbsMouseReport(x int16, y int16, buttons uint8) error {
+func (u *UsbGadget) AbsMouseReport(x int, y int, buttons uint8) error {
 	u.absMouseLock.Lock()
 	defer u.absMouseLock.Unlock()
 

usb.go

@@ -89,7 +89,7 @@ func (s *Session) rpcKeypressReport(key byte, press bool) error {
 	return gadget.KeypressReport(key, press)
 }
 
-func (s *Session) rpcAbsMouseReport(x int16, y int16, buttons uint8) error {
+func (s *Session) rpcAbsMouseReport(x int, y int, buttons uint8) error {
 	if s == nil || !s.HasPermission(PermissionMouseInput) {
 		return ErrPermissionDeniedMouse
 	}
@@ -128,7 +128,7 @@ func rpcKeypressReport(key byte, press bool) error {
 	return ErrNotPrimarySession
 }
 
-func rpcAbsMouseReport(x int16, y int16, buttons uint8) error {
+func rpcAbsMouseReport(x int, y int, buttons uint8) error {
 	if primary := sessionManager.GetPrimarySession(); primary != nil {
 		return primary.rpcAbsMouseReport(x, y, buttons)
 	}