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.

docs/book/src/guide/sketching.md

@@ -226,3 +226,22 @@ remain valid in an inch design. Angular dimensions keep their angular units. Del
 retain trailing zeros. Component/canvas distance controls and inspection, parts-library
 and flat-pattern measurements follow design units too; parameter expressions and metric
 standard names retain their explicit authored units.
+
+### Reviewing mirror, pattern, and offset results
+
+Mirror, rectangular/circular Pattern, and Offset show the active selection step in their
+shared tool window. Click an input to change it; click a selected object again or Ctrl/Cmd-click
+it to remove it. Each input has its own Clear button. Source inputs show a count, and single
+references identify the chosen mirror line, direction, or centre. Box selection also works
+while the window is open. Sketch modify tools take geometry from the sketch being edited.
+
+Proposed sketch geometry appears **green** before confirmation. Change the inputs or values to
+update the preview, then press **OK**. **Cancel** discards the preview. A circular pattern centre
+can be an existing point or a position clicked in empty sketch space.
+
+Offset distances are editable driving dimensions: double-click a dimension or change its model
+parameter to resize the offset without moving its source curves. The selected side, distance,
+and association survive save/reopen and undo/redo. Symmetric offsets share one driving distance;
+Two Sides has an independent distance for each side. Disconnected selected curves or chains are
+all offset. Breaking an association retains its current geometry and removes that association's
+driver. Older offsets retain their saved fixed distances.