Keep the mask when the photograph is closed

A local adjustment survived until the session ended and then did not exist.
Nothing reported it, because nothing had failed.

The sidecar format has carried masks since they were added, `Version::apply`
restores them into the graph, and `Version::update` captures them — that work
landed complete and was never called. The autosave writes `copy_settings()`,
which is a `Preset`: a map from (operation, parameter) to a number. A mask is
not a parameter. It is a rule about *where*, with a chain of its own, so it
fell outside the only thing being written, and the read path had nothing to
read.

The save now carries the stack beside the preset, on both the local and the
remote path. Deliberately not merged but replaced wholesale: this is the stack
as it stands, so a layer the user deleted has to leave the file too. Merging
two devices' stacks is `Sidecar::merge`'s job and belongs to sync (FR-NC-9).

A paste still carries no masks, and the `Option` is how that is said. Settings
travel between photographs; a mask does not, because it is drawn against one
frame and describes nothing on another — and `Scope` cannot express that,
since it filters parameters and a mask is not one.

The test fails against the old save path with "the mask must come back with
the photograph", which is the whole of the defect: not a crash, not an error,
just an edit that was not there in the morning.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/dr-ui/src/library_ui.rs

@@ -2475,6 +2475,10 @@ fn collect_settings_writes(
             amendment: library::Amendment::Settings {
                 preset: preset.clone(),
                 scope,
+                // A paste carries no masks, and must not: a mask is drawn
+                // against one photograph and describes nothing on another.
+                // The target keeps whatever local adjustments it already had.
+                masks: None,
             },
         })
     });