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/ui-egui/src/theme.rs

@@ -71,6 +71,8 @@ pub struct Tokens {
     pub manipulator: Color32,
     /// New surface in a feature preview.
     pub preview_add: Color32,
+    /// Proposed sketch geometry, distinct from blue selections.
+    pub preview_sketch: Color32,
     /// Removed material in a feature preview (translucent).
     pub preview_cut: Color32,
     /// Navigation cube faces, outline and labels.