Wall/fence drafting already drew an X/Z axis cross at the segment start.
Now the moving endpoint gets a single long guide line perpendicular to the
draft segment (a second cross would collide with the start cross on
axis-aligned segments), fences gain the same guides they lacked entirely,
and the 2D floor plan renders the equivalent SVG guides (cross at start,
perpendicular line at end) fed by the floorplan draft preview store.
The guide components are extracted from wall/tool.tsx into
nodes/shared/draft-axis-guides.tsx so both tools (and the fence's formerly
duplicated arc/label helpers) share one implementation.
