Release a button held on a screen even when the laser lets go between panels

While a button is held on a screen, the laser leaving it no longer takes
KWin's pointer, and an invisible catcher overlay sits on the laser whenever
it's off every panel, so the release reaches KWin at the pointer's last
spot. The pointer helper also reports the mouse's left release as a
backstop. Not yet tested in the headset.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pointer/helper/ft-pointer.cpp

@@ -103,6 +103,8 @@
 // press and collision is frozen, so dragging past a panel's edge (resizing, moving)
 // doesn't jump the cursor to free space or swap in the laser-catching dot, which made
 // SteamVR's resize snap back.
+// A left release also goes to ft-screens ("up"), which releases a button held on its
+// screens in KWin if SteamVR gave the release to some other overlay.
 //
 // Head follow (experimental, off by default; POINTER_FOLLOW=1, or the relay's "follow toggle"): the cursor
 // is carried by a reference direction, where the head faced when it last settled, and turns
@@ -691,6 +693,9 @@ int main() {
         // Hold the drag pose (tilt, frozen distance) while SteamVR finishes the drop.
         dropHoldUntil = Clock::now() + std::chrono::milliseconds(500);
         SendTo(out, "ft_pointer", "btn trigger 0");
+        // ft-screens releases a button held on its screens in KWin even when SteamVR hands
+        // the release to some other overlay (its catcher usually gets it; this is the backstop).
+        SendTo(out, "ft_screens", "up");
         if (gazeBack) gazeOwns = true, gazeBack = false;
     };
     // The left button, from the relay's "btn trigger", with gaze mode's held-back press (see