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.

viewer/isokit-view.js

@@ -280,6 +280,8 @@
       if (k !== lastK) { lastK = k; var tg = svg.querySelector(".iso-tags"); (tg || svg).style.setProperty("--iso-k", k); }
       atFit = vb.w >= fitW * 0.995;
       svg.style.touchAction = atFit ? "pan-y" : "none";
+      // an editor keeps its overlays (point handles) at their screen size
+      if (opts.onView) call(opts.onView, vb);
     }
     function apply() {
       if (!vb) return;