Payap model v2: bigger factory, shared plant room, separate water treatment

User, October 2026: the factory is too small and needs room to grow
(possibly ten more Classics), one shared hydraulic and air supply, water
treatment perhaps in a separate building connected to the galvanics lab,
and a fully equipped workshop (maintenance tools, 3D printers, maybe a
lathe and a small CNC mill).

Model (rebuilt live in FreeCAD 26.3, BIM objects, Params-driven,
parametric check plot 135->145 m and factory 112->120 m passed):
- plot 135 m (11.4 rai) with a reserve; factory 112 x 25 m, 16 bays,
  82 m visitor corridor, fire wall at 90 m;
- press hall ~870 m2: two Duplex systems (EX 50 + EX 35), the Classic,
  ten future Classic positions in two rows on a service trench;
- central hydraulics and compressed-air plant room (~62 m2);
- water treatment building 12 x 10 m behind galvanics: buried duct
  (gravity from the +1.2 m floor), covered crossing 6 m clear;
- workshop ~200 m2 with benches, tool cabinets, 3D printers, lathe,
  small CNC mill, drill, saw, welding bay, press, washer, measuring table.

Docs: galvanics (water treatment building, proposed), crane doc (workshop
fit-out; lathe and CNC mill not yet priced; corridor now 82 m),
site-candidates Payap section rewritten, README bullet.

README.md

@@ -130,10 +130,12 @@ The detail lives in dedicated documents:
 - [Payap scenario model](docs/cnx_vinyl_parametric_payap.png): a parametric
   BIM model in FreeCAD 26.3 (`docs/cnx_vinyl_parametric_payap.FCStd`,
   [isometric](docs/cnx_vinyl_parametric_payap-iso.png)) of the whole plant
-  on a square placeholder plot of Payap land: an 84 x 25 m production-only
-  factory with the five-press fleet, a separate office building for
-  offices, mastering and IT, the utility yard and site access, all driven
-  by one parameter sheet
+  on a square placeholder plot of Payap land: a 112 x 25 m production-only
+  factory with the five-press fleet, room for ten more Classics and one
+  shared hydraulic and air plant, a separate office building for offices,
+  mastering and IT, a separate water treatment building next to
+  galvanics, the utility yard and site access, all driven by one
+  parameter sheet
 - [Process logging and traceability](docs/traceability.md): end-to-end
   per-order traceability for customers, batch genealogy from audio file to
   shipment, and the requirements this sets for the factory software