Bind the two develop gestures that were described and not bound

FR-DEV-16's book said resetting a control and hiding a mask layer were
reachable by pointer and by finger, and stopped there. The reason was
honest: the generated rows have no focus, so "reset the focused control"
named a thing the panel could not point at. But a photographer at the
keyboard means something narrower than focus. They mean the slider they
just dragged too far, and that is a thing the panel can remember.

So the Adjustments global keeps the last control moved — two indices,
written where the panel forwards the change and cleared when the next
photograph opens, so a reset cannot reach back into the previous edit
through an index that happens to be shared. R puts it back, through the
same callback the track's double-click takes, and is silent until
something has moved.

The mask layer needs no such notion, because the panel already has a
selection: the rows the edge controls point at. H hides or shows those,
through the path the ring at the head of the row takes, so it is an edit
and a history step exactly as the ring is. A mixed selection goes to
shown, since the layer nobody can see is the one being asked about.

Both tags now carry the key, and the book says so.

ui/dr-ui/ui/adjust.slint

@@ -995,6 +995,18 @@ export global Adjustments {
 
     callback param-changed(int, int, float);
     callback param-reset(int, int);
+    /// TRACES: FR-DEV-16
+    /// The control last moved, so a key can put it back.
+    ///
+    /// The generated rows have no focus: they are a model the repeater
+    /// rebuilds, and a focus ring for them would be a larger change than the
+    /// binding wants. What a photographer means by "reset that" from the
+    /// keyboard is the slider they just dragged too far, and that is a thing
+    /// the panel can remember without any of them being focused. -1 is none,
+    /// which is where every photograph starts — see `lib.rs`, which clears
+    /// these on open so the key cannot reach back into the previous edit.
+    in-out property <int> touched-op: -1;
+    in-out property <int> touched-param: -1;
     /// Every parameter of one operation back to its default. A section's reset
     /// and a curve's reset are the same action, so they share the one callback
     /// rather than duplicating a handler that would have to be kept in step
@@ -1511,6 +1523,8 @@ export component AdjustPanel inherits Rectangle {
                         curve-channel: Adjustments.curve-channel;
                         drag-changed(on) => { root.slider-dragging = on; }
                         param-changed(op, param, v) => {
+                            Adjustments.touched-op = op;
+                            Adjustments.touched-param = param;
                             Adjustments.param-changed(op, param, v);
                         }
                         param-reset(op, param) => { Adjustments.param-reset(op, param); }