ERPNext runs the whole plant; every tool we build integrates with it

Decided by the user (October 2026): the whole plant runs ERPNext, and
all tooling we develop has to interact with it.

digital-factory.md: standing decision in the summary; decision 10
(ERPNext owns the business documents, the factory application owns the
floor; ERPNext names are the shared keys); new section 'ERPNext: the
plant's ERP' with the ownership table (customers, prices, sales orders,
items and BOMs, work orders and job cards per station, batches and
quality inspections per compound lot, serial numbers for metal parts,
downtime entries, delivery notes, assets, accounting, payroll vs. cycles,
per-record inspection, genealogy and the hash-chained log staying in the
factory application), the integration rules (one typed Frappe REST
client in cnx-factory, an integration user per tool, webhooks in,
transactional outbox with idempotent postings so the floor never waits
on the ERP, business-sized postings, customisation as a Frappe app in
Gitea, nightly reconciliation, no public ERPNext endpoint, new tools use
the same client), hosting on NixOS (no nixpkgs module, NixOS/nixpkgs
#241921; Avunu frappe-nix as the start, frappe_docker as
oci-containers fallback; MariaDB + Redis; vinyl-erp on site behind the
gateway proxy; OIDC sign-on; upgrades on a restored copy), Thai
localisation (Ecosoft erpnext_thailand: VAT, WHT, PND, billing notes;
Ecosoft as partner to quote; payroll and BOI reporting to check),
phasing (dev ERPNext now; accounting and assets from the first capex
invoice; manufacturing at commissioning) and estimates. ERPNext added
to the architecture diagram, services, machines (vinyl-erp), module
list, backup, cost, build order and open decisions; the old 'ERP out of
scope, decide after launch' line replaced.

artist-platform.md: price list, customers, sales orders, campaign
pledges as payment entries, through the plant's outbox. traceability.md:
one ERP, one set of keys. README summary. total-investment.md added
scope: ERPNext (to quote, not in the sum, no licence fee).

docs/traceability.md

@@ -45,6 +45,12 @@ For any order, the customer can follow the full chain:
   mother, stamper, press run, box) gets an ID, and every ID knows its
   parents. A customer complaint about one record resolves to a specific
   stamper, press, shift, and compound lot.
+- **One ERP, one set of keys**: business documents (orders, work orders
+  and job cards, lots, deliveries, invoices) live in ERPNext, which the
+  whole plant runs; the traceability detail lives in the factory
+  application and carries the same ERPNext document names, so a trace and
+  an invoice point at the same order
+  ([digital factory](digital-factory.md#erpnext-the-plants-erp)).
 - **Environment attached**: the whole-factory HVAC monitoring (temperature,
   humidity, PM per zone) is logged on the same timeline, so any production
   window can be correlated with plant conditions.