Add Vertical and Horizontal perspective sliders to Compose

The keystone existed in framing but nothing in develop could reach it:
framing is presented by its own Compose panel rather than generated, so
new framing parameters get no control until the panel names them.

Compose now has Vertical and Horizontal sliders under Straighten,
mirrored from the session like the angle, recorded as parameter steps
("Vertical Perspective" in the history), cleared by the Compose reset
and by opening the next photograph. Releasing either slider refits the
crop the way releasing the straighten slider does: a keystone alone
needs no crop, but it moves the empty corners of a straightened frame,
so the crop that avoided them before may not after, or may have room
to grow back.

ui/dr-ui/src/develop_ui.rs

@@ -1196,6 +1196,56 @@ fn wire_rotation_flips_straighten(
                 redraw(&w);
             });
     }
+    {
+        // TRACES: FR-DEV-20
+        // The keystone sliders: applied on every frame of the drag, like the
+        // angle, so the photograph follows the thumb.
+        let weak = window.as_weak();
+        let session = session.clone();
+        let redraw = redraw.clone();
+        window
+            .global::<Framing>()
+            .on_keystone_v_changed(move |amount| {
+                let Some(w) = weak.upgrade() else { return };
+                if let Some(s) = session.borrow_mut().as_mut() {
+                    s.set_keystone_v(amount);
+                }
+                sync_framing(&w, &session);
+                redraw(&w);
+            });
+    }
+    {
+        let weak = window.as_weak();
+        let session = session.clone();
+        let redraw = redraw.clone();
+        window
+            .global::<Framing>()
+            .on_keystone_h_changed(move |amount| {
+                let Some(w) = weak.upgrade() else { return };
+                if let Some(s) = session.borrow_mut().as_mut() {
+                    s.set_keystone_h(amount);
+                }
+                sync_framing(&w, &session);
+                redraw(&w);
+            });
+    }
+    {
+        // TRACES: FR-DEV-20
+        // The end of a keystone gesture refits the crop, on release only, for
+        // the reasons the straightening's does above: a straightened frame's
+        // empty corners move with the keystone.
+        let weak = window.as_weak();
+        let session = session.clone();
+        let redraw = redraw.clone();
+        window.global::<Framing>().on_keystone_committed(move || {
+            let Some(w) = weak.upgrade() else { return };
+            if let Some(s) = session.borrow_mut().as_mut() {
+                s.auto_crop_to_angle();
+            }
+            sync_framing(&w, &session);
+            redraw(&w);
+        });
+    }
     {
         // The geometry section's reset: crop, angle, rotation and flips back
         // to neutral, leaving every colour adjustment where it is. The panel's