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.

assets/styles/ui/palettes.rs

@@ -44,6 +44,7 @@ impl Tokens {
             body_edge: Color32::from_rgb(40, 44, 52),
             manipulator: Color32::from_rgb(40, 110, 220),
             preview_add: Color32::from_rgb(112, 160, 226),
+            preview_sketch: Color32::from_rgb(32, 190, 96),
             preview_cut: Color32::from_rgba_unmultiplied_const(232, 84, 44, 110),
             cube_face: Color32::from_rgb(236, 239, 244),
             cube_border: Color32::from_rgb(85, 94, 110),