Energy: PEA tariff, electric vs biomass steam, PV vs solar thermal

PEA tariff schedule (May 2023 onward, still current) filed under
docs/finance/pea/; Ft 0.1623 THB/kWh for Sep-Dec 2026 from the PEA Ft page.
The plant falls under Schedule 3.2.2 (Medium General Service, TOU, 22 kV).

New section in sustainability.md: blended ~3.81 THB/kWh for two-shift
production plus 132.93 THB/kW demand charge; electric steam ~4.7M-5.5M
THB/yr at maturity against ~0.35M-0.8M of biomass fuel; self-consumed PV
worth ~3.7 THB/kWh (~4.5-7 yr payback); solar thermal not recommended;
the battery earns little from TOU arbitrage or peak shaving. biomass.md,
scale.md, the utilities CSV note and the README follow.

README.md

@@ -89,8 +89,10 @@ The detail lives in dedicated documents:
 - [Equipment needs and supplier map](docs/suppliers/equipment-suppliers.md):
   the full needs list per production step with supplier tables and contacts
 - [Sustainability](docs/sustainability.md): the solar installation (Deye
-  inverters, 271 kWh Gobel Power battery stack), the zero contaminated water
-  commitment, and the materials strategy
+  inverters, 271 kWh Gobel Power battery stack), the PEA grid tariff and
+  what it decides (biomass steam at about a tenth of the cost of electric,
+  PV rather than solar thermal), the zero contaminated water commitment,
+  and the materials strategy
 - [Worker safety](docs/worker-safety.md): safety training, galvanics clean
   rooms and decontamination, PPE
 - [Biomass fuel strategy](docs/biomass.md): the 60 rai own-grown coppice
@@ -205,7 +207,8 @@ docs/
 │   ├── galvanics.md       Electroforming and stamper prep equipment plan
 │   └── pressing-line.md   Press fleet strategy and equipment plan
 ├── finance/               Project cost overviews, revenue model,
-│                          construction RFQ
+│                          construction RFQ, PEA electricity tariff
+│                          schedule (pea/)
 ├── suppliers/             Supplier contacts, vendor landscape, supplier map
 ├── artist-platform.md     Upload, price calculator, fan-funded pressing
 ├── biomass.md             Biomass fuel strategy and the 60 rai coppice idea