refactor: enforce the atomic ladder in dependency-cruiser (RD-29)

Add three dependency-cruiser rules that forbid upward edges inside
libs/shared/src/ui: atoms-compose-nothing-above, molecules-below-organisms,
and design-system-not-layout. RD-27 made the atomic ladder expressible by
moving components into atoms/molecules/organisms folders; these rules make
it enforced, so an upward import now fails dep:check instead of shipping.

No pathNot exemption for specs and stories: measured, zero upward edges
exist anywhere in libs/shared/src/ui today, in production code, specs, and
stories alike, so the exemption PLAN proposed has nothing to protect.

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

.dependency-cruiser.base.js

@@ -109,6 +109,29 @@ module.exports = function buildConfig(contextAllowed, appName, tsConfigFileName)
         },
       },
 
+      // --- Atomic ladder within libs/shared/src/ui (folder = layer, CLAUDE.md decision 2) ---
+      {
+        name: 'atoms-compose-nothing-above',
+        comment: 'An atom composes nothing above it — no molecule or organism. See CLAUDE.md §2.',
+        severity: 'error',
+        from: { path: '^libs/shared/src/ui/atoms/' },
+        to: { path: '^libs/shared/src/ui/(molecules|organisms)/' },
+      },
+      {
+        name: 'molecules-below-organisms',
+        comment: 'A molecule composes nothing above it — no organism. See CLAUDE.md §2.',
+        severity: 'error',
+        from: { path: '^libs/shared/src/ui/molecules/' },
+        to: { path: '^libs/shared/src/ui/organisms/' },
+      },
+      {
+        name: 'design-system-not-layout',
+        comment: 'The design system (ui/) does not depend on layout/ templates. See CLAUDE.md §2.',
+        severity: 'error',
+        from: { path: '^libs/shared/src/ui/' },
+        to: { path: '^libs/shared/src/layout/' },
+      },
+
       {
         name: 'no-testing-in-production',
         comment: