ADR-015: where a site's own data is allowed to live

ShopDB is a product several sites adopt, developed at one site against that
site's live fleet, so every feature arrives carrying West Jefferson's
hostnames, networks and share paths. A scan of plugins/ and shopdb/ returns 19
site literals, of which about 8 are a shipped default or a hardcode rather than
a comment: a kiosk URL baked into a PowerShell payload a sister site cannot
override, a WJ UNC path as the backup share default, and device.geaerospace.net
shipped as a SETTING DEFAULT - inherited silently by anyone who adopts.

The mechanisms already existed; the rule did not, so each value landed wherever
was convenient. The rule: a setting with a NEUTRAL default first, a
site-namespaced directory second, seed data third. Blank must be a working
state. Fleet-wide vocabulary such as the gea-shopfloor-* imaging types is not
site data and is out of scope - it already has a per-site override.

Enforced by an addition to check-naming-and-style.sh, which CI already runs, in
REPORT-ONLY mode. Making a 19-item backlog a hard gate the day it lands blocks
every unrelated commit until someone clears it; SITE_LITERALS_ENFORCE=1 turns
it into a gate once the listed hardcodes are done. The ADR carries that backlog,
including that the display FQDN domain is defined three times in three files.

docs/adr/README.md

@@ -27,6 +27,7 @@ Each ADR captures a single architectural decision: the context, the decision its
 | [012](ADR-012-geenforce-manifest-ownership.md) | GE-Enforce manifest ownership in shopdb | ACCEPTED |
 | [013](ADR-013-plugin-catalog-and-lean-builds.md) | Plugin catalog, curated shelf, and lean per-site builds | PROPOSED |
 | [014](ADR-014-schema-lean-per-site.md) | Schema-lean per-site builds (retire cross-plugin FKs, prune not-installed plugin tables) | ACCEPTED |
+| [015](ADR-015-site-specific-configuration.md) | Where a site's own data is allowed to live (setting, site directory, or seed) | ACCEPTED |
 
 ## Authoring