Feat/Sketch: associative pattern tools with independent directions and Flip/Center controls (#1601)

Thanks @Karl-VonRichter.

crates/doc/src/format/pending/sketch-pattern-directions.rs

@@ -0,0 +1,5 @@
+//! Sketch linear patterns save two independent live direction-line references and each
+//! direction's alignment and reversal. Even centered totals keep the original fixed and use
+//! reversal to choose which side receives the extra copy. Older patterns retain their fixed
+//! vectors and positive-direction placement through defaulted fields, so no rewrite is needed.
+//! The last release refuses this pending format instead of silently losing the references.