Conveyors and producers: goods flow from presses down the belts

- Producer (category Industry): a press making cartons, crates, drums, sacks or parts at a set
  rate per minute; its ram goes down once per item, a green / red light shows running / stopped.
- Conveyor: drawn the way it runs (new prefab meta `directed`: the Studio turns the piece from
  where the drag starts), belt width, height, rise (inclines), speed, goods and spacing; legs,
  rails and a drive motor. Corners join without overlap (the receiving belt runs through, the
  feeding one stops at its side).
- A conveyor starting on a producer's output side carries its goods at its rate; one starting at
  another's end carries on with what that one carries. The gap is speed / rate. A stopped press or
  belt stops the goods after it. Tooltips show speed, rate and source.
- The goods ride a group moving one gap per loop (no reordering), first fading in, last out.
- Script API: world_of(o, u, v), info_row(key, value); objects_on falls back to half of p.d.
- Theme: industry colours, LED colours (the marker's LED had none).
- examples/factory + Factory demo in the web Studio; MCP instructions on production lines.

Checks: 68 Rust tests (conveyor joints, feed and spacing, every view of the factory demo),
Studio 108/108 (draw direction, feed from a producer, rate change), web 89/89.

crates/isokit-script/src/api.rs

@@ -652,6 +652,16 @@ pub(crate) fn register_scene(e: &mut Engine, st: &Shared) {
             tag(&s, x, y, z, t, n(&p)?, Some(id), k)
         },
     );
+    // a row more in the tooltip of the object being drawn
+    let s = st.clone();
+    e.register_fn("info_row", move |k: D, v: D| {
+        let mut b = s.borrow_mut();
+        if let Some(id) = b.obj.clone() {
+            if let Some(i) = b.scene.info.get_mut(&id) {
+                i.rows.push((k.to_string(), v.to_string()));
+            }
+        }
+    });
     let s = st.clone();
     e.register_fn("info", move |id: &str, name: &str| {
         s.borrow_mut().scene.info(id, name, "")
@@ -933,7 +943,8 @@ fn register_objects(e: &mut Engine, st: &Shared) {
                 let m = d.read_lock::<Map>()?;
                 let l = xf_of(&m).inv(x, y);
                 let half = prop(&m, "w").unwrap_or(1.0) / 2.0;
-                let lim = prop(&m, "t").unwrap_or(0.0) / 2.0 + tol;
+                // half the thickness (walls), else half the width (conveyors)
+                let lim = prop(&m, "t").or_else(|| prop(&m, "d")).unwrap_or(0.0) / 2.0 + tol;
                 (l[0].abs() <= half + 1e-6 && l[1].abs() <= lim + 1e-6)
                     .then(|| with_uv(d, l[0], l[1]))
             })
@@ -1008,4 +1019,9 @@ fn register_objects(e: &mut Engine, st: &Shared) {
         let p = xf_of(&o).inv(n(&x)?, n(&y)?);
         Ok(vec![Dynamic::from_float(p[0]), Dynamic::from_float(p[1])])
     });
+    // the world plan point of (u, v) in object o's frame
+    e.register_fn("world_of", |o: Map, u: D, v: D| -> RR<Array> {
+        let p = xf_of(&o).p(n(&u)?, n(&v)?);
+        Ok(vec![Dynamic::from_float(p[0]), Dynamic::from_float(p[1])])
+    });
 }