Add undo/redo stack (Cmd+Z / Cmd+Shift+Z)

Regenerate library for rotated grid (27 designs)

Rotate staircase grid 90° clockwise (34×18, notch upper-right)

Add refined Moss & Stone v2 (9.5/10) and Tree Rings v2 (9/10)

Add 14 designs from 5-agent parallel exploration (26 total)

Re-implement design library with 12 v3 designs

Fix: add click targets for empty cells so tiles can be placed anywhere

Full grid rewrite: doubled resolution with multi-size tile support

Fix rectangle tiles: solid glazes, not arcs

Fix rectangle tile preview in picker — show SVG arc swatch

Add stamp-and-repeat tool + restore rectangle tile types

Merge branch 'layout-resize'

Resize staircase layout to 9x17 grid with 4x6 notch

Sub-grid refactor: doubled grid resolution for rectangle tile support

Add real glaze textures for rectangle tiles