[client] input: fix automatic keyboard capture

Treat autoCapture as keyboard ownership while the pointer is inside the
guest viewport. Predict the next local position for both absolute and
relative motion, then release the keyboard before the pointer crosses
an edge.

Keep capture, focus, and deferred evdev transitions consistent while
retaining the latest local position as the prediction baseline.

client/src/core.h

@@ -40,6 +40,7 @@ bool core_startFrameThread(void);
 void core_stopFrameThread(void);
 void core_handleGuestMouseUpdate(void);
 void core_handleMouseAbsolute(void);
+void core_handleMousePosition(double x, double y);
 void core_handleMouseGrabbed(double ex, double ey);
 void core_handleMouseNormal(double ex, double ey);
 void core_resetOverlayInputState(void);