Data centres: multi-storey shell, racks and pods, cooling, fire safety, power

datacentre.rhai (palette groups Data centre, Cooling, Fire safety, Power):

- dc_building: multi-storey shell (storeys of storey_h), walls in pieces,
  slabs, roof with parapet, louvres, front door and loading dock; levels
  cut it open storey by storey
- raised_floor; rack_row and dc_pod (cabinets by U, width, depth,
  equipment, fill, doors, LEDs; in-row coolers; cold / hot aisle
  containment with vent tiles, roof, end doors, ceiling duct, airflow);
  dc_cage for colocation
- crah, chiller (air-cooled, dry, adiabatic), cooling_tower, pipe_run
- smoke_detectors (grid + coverage), fire_pipe (VESDA, sprinkler, gas),
  gas_bank (Novec 1230, FM-200, Inergen sized for its halls), fire_device
  (panels, call points, abort switches, beacons, extinguishers)
- power_cab (UPS, battery, PDU, switchgear, RPP), busway, cable_tray,
  transformer
- tooltips sum IT load, kW/m2, cooling redundancy per storey, UPS load,
  battery runtime, plant cooling and agent quantity (warning when short)

Engine and stdlib:

- part_hidden(o) in house.rhai: parts on closed storeys inside a
  dc_building are not drawn (they only made sort cycles under the slab
  above); house parts, furniture and people use it. Existing examples
  render byte-identical.
- overhead services sort in their own "ceiling" layer with tight boxes
- sort records which sprites each broken cycle involved; isokit check
  names them (Rendered.cycle_at)

examples/datacentre (three storeys and a roof plant), Data centre demo in
the web Studio, tests, SCRIPTING/README/ROADMAP, MCP instructions.

README.md

@@ -40,8 +40,9 @@ isokit build C:/dev/myproject/site-view   # dist/index.html, no server needed
 
 Try the demos: `isokit studio examples/demo` (a works site),
 `isokit studio examples/house` (a furnished house built from parts),
-`isokit studio examples/factory` (presses, conveyors and robot arms) and
-`isokit studio examples/streets` (sidewalks, curves, junctions, a roundabout).
+`isokit studio examples/factory` (presses, conveyors and robot arms),
+`isokit studio examples/streets` (sidewalks, curves, junctions, a roundabout) and
+`isokit studio examples/datacentre` (a three-storey data centre).
 
 ### Studio (for everyone)
 
@@ -102,6 +103,30 @@ rounded, and the movers pass in front of and behind trees and houses as they
 go. The streets demo has traffic round the block, a bus, motorbikes, cyclists
 and people strolling.
 
+**Data centres** (palette groups Data centre, Cooling, Fire safety, Power):
+the DC building is the shell of a multi-storey data centre (storeys of the
+project's `storey_h`, 5 m in the demo); GF, 1F, 2F cut it open, and parts on
+closed storeys are not drawn at all. On each storey a Raised floor (0.6 m
+tiles over the supply plenum) carries Rack rows and Rack pods: cabinets of
+any width, depth and height in U (servers, storage, GPU, network or empty,
+mesh, glass or solid doors, status LEDs), in-row coolers between groups of
+racks, and pods with cold aisle containment (vent tiles, glass roof, sliding
+end doors, cold air rising) or hot aisle containment (backs to the aisle,
+optional duct to the ceiling); Cages for colocation. Cooling: CRAH / CRAC
+units, chillers and dry or adiabatic coolers with fan rows, cooling towers
+with a plume, flow and return pipe runs. Fire safety: detector grids with
+their coverage, VESDA sampling pipes with the detector unit, pre-action
+sprinkler and gas discharge pipes, clean-agent cylinder banks (Novec 1230,
+FM-200, Inergen), alarm and release panels, call points, abort switches,
+beacons, extinguishers. Power: UPS, battery, PDU, switchgear and RPP
+line-ups, busways with tap-off boxes, cable trays and fibre ducts,
+transformers. The tooltips do the sums: IT load per pod, floor and building,
+kW/m², cooling against load per storey (N+1 and so on), UPS loading,
+battery runtime, the agent a gas bank needs for its halls (a warning label
+when it is short). `examples/datacentre` (Data centre demo in the web Studio)
+has a power room, a hall with cold aisle pods, a GPU hall with hot aisle pods
+and cages, and chillers on the roof.
+
 **Fences and walls** around the plot: the Fence has six designs (mesh, wooden
 boards, steel bars, mesh on a stone base, cobble wall, brick wall with
 pillars). Fences and site walls whose ends meet join like house walls: corners