Payap scenario: Part/Draft model with roof, rooftop PV and PV parking canopies

New FreeCAD model docs/cnx_vinyl_parametric_payap_parts.FCStd: the Payap
scenario rebuilt from plain Part solids and Draft (arrays, labels,
dimensions) on the same Params sheet, no BIM objects, plus:

- monopitch roof 10 deg, low eave 7.0 m south, high side 11.4 m north
  (phase 1 RFQ geometry); gables and the fire wall follow the roof
- rooftop PV: 901 x 580 W placeholder modules, ~523 kWp, 17 rows in
  blocks of four with walkways, 1 m edge strip, 2.5 m clear over the
  fire wall (estimate)
- car canopy (10 bays, 72 modules) and scooter canopy (30 spaces,
  22 modules), ~54 kWp, RFQ footprints and heights
- module counts and kWp as sheet expressions; ~577 kWp in all

FreeCAD 26.3 RC1 does not propagate spreadsheet edits: CNX_apply_Params
macro touches the dependents and recomputes; parametric test (factory
length, pitch, car bays, walkway) matches the sheet counts.

site-candidates.md: roof/PV/canopy section with the export, battery and
BOI questions a 577 kWp array raises; mirrors in sustainability.md and
scale.md; README layout lines.

docs/sustainability.md

@@ -106,6 +106,11 @@ large-format modules reach roughly 225 W/m². Roughly 70 m of plot depth
 remains undeveloped behind the building for ground-mount, which matters if
 the electric-boiler route is chosen.
 
+On the Payap scenario plot the 128 m factory roof takes ~901 modules
+(~523 kWp) and the car and scooter canopies another ~54 kWp, ~577 kWp in
+all; what that size means for export, the battery and BOI is in
+[site candidates](site-candidates.md#roof-pv-and-parking-canopies-part-and-draft-model-october-2026).
+
 ### Energy efficiency architecture: recover before generating
 
 The deepest efficiency in this plant comes from its own thermodynamics: the