test(backend): split RuleTests.cs by aggregate, refresh DDD doc (WP-71)

RuleTests.cs held five aggregates' rules as nested classes in one file,
misaligned with Domain/<Aggregate>/ and with the Acceptance/Builders/
folder convention WP-70 started. Split into Domain/<Aggregate>RuleTests.cs
(pure move — same names, same bodies, same count) plus a new
ApplicationRuleTests.cs (the enum invariant moved out of the
WebApplicationFactory-booting ApplicationTests.cs, since it's a pure
Enum.GetNames check with no business needing a web host) and
OrgTemplateRuleTests.cs (RejectDraft had no direct unit test before,
only endpoint coverage).

libs/shared/docs/layers.mdx still taught the pre-WP-67 shape (six
contexts, no apps/libs split, enforcement via ESLint) — updated to the
real monorepo structure and to dependency-cruiser as the actual
enforcement mechanism. Adds specs for registration.policy.ts's
isStatusConsistent (untested; its backend mirror is) and both apps'
auth/domain/session.ts.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/ssp/src/app/herregistratie/ui/intake-wizard/intake-wizard.component.spec.ts

@@ -10,6 +10,14 @@ import { IntakeState } from '@herregistratie/domain/intake.machine';
 // wrapping is dropped, the inputs revert to bare white. The buitenland step with
 // buitenlandGewerkt='ja' has two groups (the question + the land/uren follow-up), so it
 // must render ≥2 fieldsets, each holding a form-group.
+//
+// SANCTIONED TestBed exception (CLAUDE.md "Testing": UI is normally exercised via Storybook,
+// not heavy component tests): this pins the *count and nesting* of rendered DOM nodes for a
+// specific machine state (2+ <fieldset> wrappers, each containing a .form-group), which is a
+// structural/visual regression, not an accessibility one — a Storybook a11y (axe) run checks
+// for accessibility violations on whatever markup is rendered, it does not assert that the
+// markup takes this particular shape, so it would not catch the grouping silently collapsing
+// back to bare inputs.
 const buitenlandJa: IntakeState = {
   tag: 'Answering',
   answers: { buitenlandGewerkt: 'ja' },