Projection chips redraw the preview; auto-crop as the DNG default crop

Picking a chip stored the choice for the merge and changed nothing on
screen — the chip did not even highlight, since the selected property
was never written back. Now the pick is reflected, and the job, waiting
for its decision, takes a Preview request, draws the alignment on the
chosen surface at proxy cost and reports again; the drain puts the new
picture and its size up. Auto is the surface the field of view suggests.

Also:
The largest rectangle inside the frames' coverage is found a row at a
time — a histogram of consecutive covered rows and a stack pass per row —
so the composite is never held to be measured (FR-MRG-11). It is written
as DefaultCropOrigin/DefaultCropSize (FR-MRG-4): the file opens on the
picture, the border is still in it, and resetting the crop shows it.
rawler reports the crop as the picture, which the test checks.

FR-MRG-4 records the question raised the same day — fill the border
rather than crop it — as open: a non-generative fill through the heal,
or a generative inpainter with its licence and weights. Neither decided.

core/dr-export/src/lib.rs

@@ -26,6 +26,7 @@ use dr_types::{ColourSpace, ExportFormat, ExportSettings};
 
 mod dng;
 mod encode;
+mod inscribed;
 mod error;
 mod exif;
 pub mod icc;
@@ -35,6 +36,7 @@ mod sharpen;
 mod size;
 
 pub use dng::{write_linear_dng, DngProfile};
+pub use inscribed::{Inscribed, Rect};
 pub use error::ExportError;
 pub use metadata::SourceMetadata;
 pub use name::{resolve_name, NameContext};