Routes: movers along waypoints (roadmap 8)

New route prefab (routes.rhai): cars, buses, motorbikes, cyclists, people,
deer or elephants move along waypoints, round a loop or there and back.
Each way keeps to the left of the line (or right), corners are rounded
into pieces of at most 45 degrees; there-and-back routes become loops with
U-turns, so the two directions never share a strip.

Engine: Prim::Travel / sprite.begin_travel / script travel(a, b, dur,
windows) ... end(): the mover is drawn at a piece's start and slides to
its end while it is on that piece, hidden otherwise. The renderer writes
keyframes per piece (named by a hash of their content) into one <style>
per view. Each piece is its own sprite with the lane strip as its sort
extent (ext_reset), mitred at the corners, so movers pass in front of and
behind trees, lamps and houses. Movers that look alike and never meet on
a piece share one drawing. iso-travel pauses (not hides) in still,
reduced-motion and ghosted views.

Studio: meta shape "path" draws point by point (snapping like runs) and
saves one object with pts; ending on the first point closes the loop.
MCP: pts in the object schema, route guidance.

Demos: streets gets traffic round the block, a bus, motorbikes, cyclists
and strolling people (replacing the one-axis cars); country gets cars on
the lane.

Tests: Rust 79 (each mover on exactly one piece at every moment, in every
rotation), Studio 125, web 99.

crates/isokit-project/src/mcp.rs

@@ -29,6 +29,9 @@ fences, hedges, house walls) can run at any angle: a piece from (x0, y0) to (x1,
 w = the distance and rot = atan2(y1 - y0, x1 - x0) in degrees; where diagonal pieces meet, corners are mitred. \
 Animals (category Animals: deer, boar, fox, elephant, rabbits, birds, butterflies) are herds: props.n animals \
 scattered within props.r metres of x, y, facing about the rotation; keep them out of roads, ponds and buildings. \
+A route (type route) moves props.n movers (props.kind: car, bus, motorbike, cyclist, person, deer, elephant) along \
+waypoints pts (relative to x, y): round them when props.closed, else there and back; each way keeps to the left \
+of the line (props.keep). For traffic, put the points on the road centre lines; keep routes clear of buildings. \
 Production lines (category Industry): a producer (props.rate per minute, product) puts goods out on its local +x \
 side; a conveyor (rot 0 runs towards +x, 90 +y, 180 -x, 270 -y; w = length, props.speed m/s) starting exactly \
 at that side carries them, and a conveyor whose start is at another's end carries on with them (corners join). \
@@ -58,6 +61,8 @@ pub fn tools() -> Vec<Value> {
         "info": { "type": "string", "description": "tooltip text" },
         "tag": { "type": "string", "description": "label pinned above the object" },
         "levels": { "type": "array", "items": { "type": "string" }, "description": "levels it shows on (empty: all)" },
+        "pts": { "type": "array", "items": { "type": "array", "items": { "type": "number" }, "minItems": 2, "maxItems": 2 },
+                 "description": "points [[x, y], ...] relative to x, y (in the object's turned frame): a route's waypoints, an area's outline" },
     });
     let mut add = obj_fields.as_object().unwrap().clone();
     add.insert("type".into(), json!({ "type": "string", "description": "prefab type, e.g. building, tree, car (list_prefabs)" }));