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.

docs/equipment/galvanics.md

@@ -85,6 +85,15 @@ What this changes in the plan:
     [facility security](../facility-security.md) (no extraction, no
     plating) applies to every one.
   - Compressed air at 6 bar for the PASU; drains Ø32 mm.
+- **Water treatment in its own building (proposed, October 2026).** The
+  zero-discharge effluent treatment, the DI water plant and the chemical
+  store move out of the factory into a small building next to the
+  galvanics room. A buried service duct carries the effluent by gravity
+  from the galvanics floor at +1.2 m and brings DI water back, and a
+  covered crossing joins the two doors. The galvanics room keeps only a
+  chemical day store at the duct head. The
+  [Payap scenario model](../site-candidates.md#payap-scenario-model-october-2026) draws it as a 12 × 10 m building
+  (estimate).
 - **Space.** One of each unit is ~5.6 m² of footprint (PASU 1.56, PMPB
   1.23, PPPU 1.32, PDPU 1.44 m²), plus 500 mm service access behind the two
   tank units and working space around them: comfortably inside the 80 to