feat(arch): WP-38 — dependency graph + declarative boundaries (dependency-cruiser)

Adopt dependency-cruiser as the single declarative source for bounded-context +
atomic-layer boundaries, replacing the per-context no-restricted-imports blocks that
had to be hand-copied (and had left herregistratie uncovered). `.dependency-cruiser.js`
encodes context direction (everyone→shared, herregistratie→registratie, showcase→*),
domain-purity, contracts-import-nothing, ui↛infrastructure, ApiClient confinement, and
no-circular. `npm run dep:check` enforces (wired into ci-local.sh + the frontend CI job);
`npm run dep:graph` emits a committed mermaid context×layer graph. ESLint slimmed to
no-explicit-any + template a11y. Docs + new-context skill updated to the single source.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/ci-local.sh

@@ -12,6 +12,7 @@ cd "$(dirname "$0")/.."
 step() { printf '\n\033[1;36m▶ %s\033[0m\n' "$1"; }
 
 step "lint";                      npm run lint
+step "dependency boundaries";     npm run dep:check
 step "format:check (prettier)";   npm run format:check
 step "check:tokens";              npm run check:tokens
 step "test (vitest)";             npm test