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/SCRIPTING.md

@@ -168,6 +168,15 @@ spread within `r` of the object, each facing its rotation give or take 70°,
 each its own sprite. Flocks of birds, butterflies and bees use `swim` with a
 `shape`.
 
+## Points (`pts`)
+
+An object's `pts` are plan points relative to its x, y in its turned frame. A prefab that draws
+them as its outline sets `outline: true` in its meta (Area): the Studio then offers Edit corners,
+which turns its `w` x `d` rectangle into four points, and Rectangle again, which removes them.
+Every selected object with `pts` shows handles: drag a point, drag the + of a side to add one,
+double-click a point to remove it (an open route keeps 2, a closed outline 3). Route points say
+whether they close with `props.closed`; any other `pts` are a closed outline.
+
 ## Groups and the drawing order
 
 Objects of type `group` are never passed to scripts (they draw nothing), nor is anything inside a