Add Payap University land as a site candidate

Payap University (Chiang Mai) is interested in leasing land to the
project; a pharmaceutical facility is under construction on the same land.

New docs/site-candidates.md puts the three options side by side (Mueang
Chi lease, Northern Region Industrial Estate, Payap) with the public facts
on Payap (Mae Khao campus on the Chiang Mai-Lampang superhighway, bought
as low-lying land, ~275 acres; Faculty of Pharmacy cosmetics production
facility tendered July 2024; RPAH cannabis/herbal bioreactor centre), why
it is attractive (5 km from the old city, a university partner with music,
pharmacy and labs, production already being built there) and the checks
that could rule it out, in order: zoning for pressing, boiler and later
electroplating; whether the university can lease to a company; the GMP
neighbour's sensitivity to our emissions (argues against biomass steam
there); flooding; plot fit; galvanics consent. Questions for the next
meeting listed. Nothing re-sited: model, RFQ and site code stay on
Mueang Chi until a plot is known.

README (intro, bullet, layout), roadmap item 9 and the lease fork in
project-timeline link to it.

docs/roadmap.md

@@ -57,7 +57,9 @@ These three run in parallel and gate everything downstream:
    confirm the EPC (Solar Nicolo or other) warrants a mixed-vendor DC bus
 9. **Site selection**: candidate buildings/plots in Lamphun and Lampang
    (Northern Region Industrial Estate first for its shared effluent
-   treatment and licensing simplicity), screened against the
+   treatment and licensing simplicity) and, since October 2026, Payap
+   University land in Chiang Mai ([site candidates](site-candidates.md)),
+   screened against the
    [scale requirements](scale.md): 6 to 8 rai, 1,400 to 2,000 m² single
    story (including the workshop and visitor corridor), multiple tons per
    m² slab, 500 to 1,000 kVA connection, and a frame able to carry an