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>

.github/workflows/ci.yml

@@ -27,6 +27,8 @@ jobs:
           cache: npm
       - run: npm ci --prefer-offline --no-audit --no-fund
       - run: npm run lint
+      # Bounded-context + atomic-layer boundaries (WP-38, dependency-cruiser).
+      - run: npm run dep:check
       - run: npm run format:check
       - run: npm run check:tokens
       - run: npm test