Sketch: associative, editable sketch patterns (#1103)

Rectangular and circular sketch patterns stay linked to their source: editing the pattern's count, spacing or the source geometry updates the copies, and the copies keep their point and radius relations. Patterns are saved under format 20; older designs keep their independent copies.

docs/book/src/guide/files.md

@@ -73,7 +73,7 @@ is available. Missing or incompatible pictures use the usual thumbnail generatio
 The default `cache: false` omits the portable thumbnail too.
 The repository's `docs/design-container.md` describes limits and encoding details.
 
-Current designs use format 20, including thin extrudes, sheet metal perforation fields, editable associative offset-distance dimensions, the style of sketch text (bold, italic, alignment, spacing and the curve it follows), face anchors on a piece of a face by its own name, sheet metal rims and bend ends, bend edges for Convert to Sheet Metal, the tear corner relief of sheet metal rules, the names of projected edges, physical materials defined in the design, the font of sketch text, sheet metal corner relief shapes, sketch face anchors on cylinder caps, sketch axis
+Current designs use format 20, including thin extrudes, sheet metal perforation fields, associative editable sketch patterns, editable associative offset-distance dimensions, the style of sketch text (bold, italic, alignment, spacing and the curve it follows), face anchors on a piece of a face by its own name, sheet metal rims and bend ends, bend edges for Convert to Sheet Metal, the tear corner relief of sheet metal rules, the names of projected edges, physical materials defined in the design, the font of sketch text, sheet metal corner relief shapes, sketch face anchors on cylinder caps, sketch axis
 links, persistent
 names from exact face history, exact planar shell-face anchors, persistent analytic offset boundary roles and
 association profile references, durable sketch face anchors, periodic fit splines and versioned

docs/book/src/guide/sketching.md

@@ -246,6 +246,17 @@ Proposed sketch geometry appears **green** before confirmation. Change the input
 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.
 
+Sketch patterns keep each instance related to the seed geometry: moving the seed updates the
+copies, and a copy cannot deform independently. Circle and ellipse radii follow the seed too.
+Choose a circle's centre point to keep a circular pattern centred on that circle. A centre
+placed in empty space becomes a sketch point that can be dimensioned or made coincident.
+Double-click the pattern badge (at the circular centre or beside the rectangular seed), or
+right-click a seed or copy and choose **Edit Sketch Pattern**, to change quantity, spacing,
+direction or total angle. Confirmed edits preserve surviving instance ids; Cancel discards
+the preview. Pattern settings survive save/reopen and undo/redo. Deleting a seed, copy or
+pattern relation breaks that association and leaves the remaining geometry independent.
+Patterns saved by older versions remain independent copies; recreate them to add associations.
+
 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;