Point handles for routes and outlines; Area corners; bus goes round right

Studio: one selected object with pts (a route, an outlined area) shows a
handle on each point and a + in the middle of each side: drag a point to
move it, drag a + to add one there, double-click a point to remove it
(open routes keep 2, outlines 3). Points snap to the grid and onto wall,
fence and road ends, at any angle; one undo step each. Handles keep their
screen size (new viewer callback onView on every redraw) and follow
re-renders and selection. The viewer captures the pointer, so a double-
click targets the drawing: the last point pressed is remembered instead.

Prefab meta `outline`: the prefab draws pts as its outline. Area has it:
Edit corners turns its rectangle into four points, Rectangle again
removes them.

Routes: where a path doubles back, the lane offset puts a point on each
side, so it rounds into a U-turn instead of a diagonal across the lanes.
The streets demo bus now runs east, three quarters round the roundabout
(clockwise, left-hand traffic), down south street, turns and comes back
by the short way, instead of going round the wrong way on its way out.

Tests: Rust 81 (a doubling-back route: each mover once, no sort cycles),
Studio 134 (corners, move, add, remove, undo), web 100.

docs/ROADMAP.md

@@ -162,8 +162,9 @@ per row, Ctrl+G / Ctrl+Shift+G, drag rows to reorder or into a group, ▲ ▼ an
 ## Phase 2: richer editing
 
 - [x] Interior prefabs (see Build your own house); a building `rooms` prop is still open
-- [ ] Path objects in the Studio: click points for areas, roads (polyline with width), fences, walls,
-      pipe runs; vertex handles (routes are drawn point by point: meta `shape: "path"`)
+- [ ] Path objects in the Studio: click points for roads (polyline with width), fences, walls, pipe
+      runs. Done: routes drawn point by point (meta `shape: "path"`); point handles on every object
+      with `pts` (move, add on a side, double-click removes); areas get Edit corners (meta `outline`)
 - [x] Multi-select (box select, Ctrl+click, Shift range), group move, turn, copy, delete, edit
 - [x] Groups in the object tree (fold, hide, lock, drag in and out) and the drawing order (drag, ▲ ▼)
 - [ ] Align / distribute the selection