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.

README.md

@@ -53,6 +53,7 @@ Try the demos: `isokit studio examples/demo` (a works site),
 | Several | Ctrl+click (map or list) adds or takes out one, Shift+click in the list a range, Shift+drag on the map a box, Ctrl+A all; then drag one to move them all, arrows, R, Ctrl+D, Delete and the property form work on all of them |
 | Group | select several, then ▤ Group or Ctrl+G; Ctrl+Shift+G ungroups. In the object list a group folds open and shut, a click on it selects all of it (drag one on the map to move them all), its eye and lock hide or lock all of it; drag rows into or out of a group |
 | Order | the object list is the drawing order of ground pieces (areas, beds, ponds, roads): higher lies on top. Drag rows, or ▲ ▼ / Ctrl+] Ctrl+[ (with Shift: to the front / back) |
+| Points | a selected route or outlined area shows its points: drag one to move it, drag a + (middle of a side) to add one, double-click one to remove it; points snap to the grid and onto wall, fence and road ends. An Area's Edit corners turns its rectangle into points |
 | Move | drag it, or arrow keys by the snap step (0.1 / 0.5 / 1 / 5 m) |
 | Turn | R / Shift+R or ⟲ ⟳ (quarter turns), or type any angle in Rotation |
 | Edit | the right panel: size, storeys, colours, solar, tooltip text, label, levels |