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.

README.md

@@ -38,8 +38,9 @@ isokit studio C:/dev/myproject/site-view  # opens the editor in the browser
 isokit build C:/dev/myproject/site-view   # dist/index.html, no server needed
 ```
 
-Try the demos: `isokit studio examples/demo` (a works site) and
-`isokit studio examples/house` (a furnished house built from parts).
+Try the demos: `isokit studio examples/demo` (a works site),
+`isokit studio examples/house` (a furnished house built from parts) and
+`isokit studio examples/factory` (presses and conveyors).
 
 ### Studio (for everyone)
 
@@ -192,6 +193,12 @@ the footprint, and `rot` turns the object in 90° steps. Levels: `site` (or any
 other id) shows buildings closed, while `gf`, `1f`, `2f` … cut them open at that
 storey.
 
+Production lines: a Producer (category Industry) makes goods at a set rate
+and puts them out on its +x side; Conveyors drawn from there carry them on,
+round corners and up inclines, each at its own speed, so the gap between goods
+follows rate and speed. Tooltips show the numbers. `examples/factory` (Factory
+demo in the web Studio) has a few lines.
+
 Animations (fans, smoke, fish, traffic) step on about ten times a second by
 default ("light"): running CSS animations repaint the whole drawing every frame,
 which keeps a slow laptop busy. The ▷ button in the view toolbar switches
@@ -224,6 +231,7 @@ studio/                the Studio GUI (served by `isokit studio`, and by the web
 web/                   web Studio shell: WASM backend for studio.js, projects, folders, zip, code editor
 examples/demo          demo project (works site)
 examples/house         house built from parts (walls, windows, doors, floors, furniture, roof)
+examples/factory       production yard: producers and conveyors
 deploy/Caddyfile       the web Studio's vhost on the buildfor.life web server (s1)
 ```