Say so when a crop leaves a mask outside the frame

Cropping tighter past a mask layer made it invisible without a word:
the layer stayed in the panel and the sidecar, and its adjustment went
on landing on pixels nobody would see again.

When a crop is let go, develop now measures what the gesture did to the
mask stack (dr_pipeline::orphan) and, if any layer is now entirely or
mostly outside the frame, shows a notice over the photograph: how many
layers, their names, "Undo crop" and "Keep crop". The crop is already
applied and nothing waits on the answer.

The crop overlay gains a release callback carrying the rect the press
began from, so the measurement runs once per gesture and never on the
drag's per-frame changes. Choosing a ratio is measured the same way,
being a crop committed in one click.

"Undo crop" is the ordinary undo, and the notice is tied to the history
revision it was raised at: the redraw that follows any history move
clears it, so the crop and its warning go back as one step. A second
drag folded into the same step is measured from where that step began.
A crop that strands nothing shows nothing.

ui/dr-ui/src/develop/session.rs

@@ -107,6 +107,10 @@ pub struct DevelopSession {
     /// comparison is held. Viewing state: nothing about the edit changes,
     /// and it goes down with the session.
     pub(super) compared_snapshot: Option<String>,
+    /// TRACES: FR-DEV-17
+    /// The layers the last committed crop took out of the frame, while the
+    /// history still stands on that crop. See [`super::framing::CropNotice`].
+    pub(super) crop_notice: Option<super::framing::CropNotice>,
     pub(super) demosaiced: Arc<DemosaicedImage>,
     pub(super) adjust: AdjustPass,
     /// TRACES: FR-DSP-7
@@ -373,6 +377,7 @@ impl DevelopSession {
             snapshots: Vec::new(),
             removed_snapshots: Vec::new(),
             compared_snapshot: None,
+            crop_notice: None,
             demosaiced: Arc::new(demosaiced),
             adjust: AdjustPass::new(ctx),
             histogram: HistogramPass::new(ctx)