Keyboard clicks at the gaze: Meta+J and Meta+K

gaze_left and gaze_right (Meta+J and Meta+K by default) click where you look.
A tap clicks where the dot was at the press and tells the gaze tracker it was
right there. Held, the pointer stays put in your view, so turning your head
carries it onto the target; the release clicks there and the correction is a
lesson (judged by the net correction, not the head's path). Held still for
POINTER_GAZE_HOLD it's a real press that the head drags, and Meta+K while
Meta+J aims presses where the dot is now, to correct and then drag.

A Meta combination now also sends the desktop an F24 press and Meta's release
at once: Meta's release no longer opens Plasma's launcher, and the click isn't
Meta+click (KWin's window move and resize, which swallowed right clicks). The
desktop gets Meta back for the next key if it's still held.

Also fixes e16b758, which had taken the gaze actions off the key combination
list along with the controllers'; and gaze_quickcal (the gaze service's
one-dot check) joins the actions.

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

input-settings/main.qml

@@ -842,9 +842,11 @@ Kirigami.ApplicationWindow {
                 Controls.Label {
                     Layout.maximumWidth: Kirigami.Units.gridUnit * 30
                     wrapMode: Text.WordWrap
-                    text: "Gaze works with the mouse. The Frame controllers don't take part, and moving one hands the "
-                          + "pointer back to the controllers. Gaze pointer on/off, Gaze precision, and Gaze drag can go on "
-                          + "a mouse button (Buttons page) or a key combination below."
+                    text: "Gaze works with the mouse and the keyboard. Keyboard clicks (Meta+J left, Meta+K right by "
+                          + "default): tap to click where you look, or hold, turn your head until the dot sits on the "
+                          + "target, and let go; hold still to drag. The Frame controllers don't take part, and moving "
+                          + "one hands the pointer back to them. Gaze pointer on/off, Gaze precision, and Gaze drag can "
+                          + "also go on a mouse button (Buttons page)."
                     opacity: 0.7
                     font: Kirigami.Theme.smallFont
                 }