Guide sketch patterns with live previews and editable offsets (#966)

Sketch Mirror, rectangular and circular Pattern, and Offset now show a green live preview that follows the selection and settings; OK commits, Cancel leaves the sketch unchanged. The shared dialogs show the current selection step and source counts, sources can be toggled with Ctrl/Cmd-click, cleared and reselected.

Offsets keep editable driving distance dimensions (One Side, Two Sides, Symmetric) that update the derived curves without moving the source, with undo/redo and save/reopen. Format 19: older files keep their fixed offsets.

New dialog labels in en, zh, ja, de and ko.

Fixes #696. Fixes #517.

crates/sketch/src/offset_topology.rs

@@ -829,6 +829,7 @@ impl Sketch {
             }
         }
         candidate.offsets.remove(index);
+        candidate.constraints.retain(|c| !matches!(&c.kind, crate::ConstraintKind::OffsetDistance { output, .. } if record.owns_output(output)));
         for point in owned {
             if point != 0
                 && candidate.curves.iter().all(|c| !c.kind.uses(point) || outputs.contains(c.id.as_str()))