Add a 'Copy from existing' option to the New Canvas modal. It lists every
canvas with node/group/text counts; picking one deep-copies its nodes, edges,
parent/child links and canvas state (viewport, custom style, floor plan) into
a fresh design.
Backend: POST /designs/{source_id}/copy remaps node ids, re-points edges and
parent links, and clones canvas state; GET /designs now returns per-design
counts for the picker. Standalone mode clones the localStorage canvas.
Closes#216
ha-relevant: maybe
- Fix ApiEdge type: add 'basic' to animated union
- Add 5 standalone storage tests: properties, empty properties, waypoints,
basic animation, and all three animation types round-trip through localStorage
Pouzor