test(a11y): @axe-core/playwright smoke check for major pages

Phase 4 — wires `@axe-core/playwright` into the smoke suite so any
critical/serious WCAG 2.1 A/AA violation on the main authenticated
pages fails CI.

tests/e2e/smoke/20-accessibility.spec.ts:
  Iterates 6 routes (dashboard, clients, yachts, interests, berths,
  admin/branding) — each navigates after login, waits for
  networkidle, runs AxeBuilder with WCAG2/2.1 A+AA tags, asserts no
  critical/serious violations.

  DISABLED_RULES list trims two known-noisy rules that fire on Radix
  primitives + design-pass-pending muted text:
    - tabindex  (Radix focus traps)
    - color-contrast  (muted body text, pending design pass)

  The list is intentionally small; new entries require a comment and
  an audit. Easier to widen than narrow.

Run: pnpm exec playwright test --project=smoke

No vitest impact (1298/1298 still green); the spec only runs on the
e2e playwright project so the unit suite stays fast.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -114,6 +114,7 @@
     "zustand": "^5.0.13"
   },
   "devDependencies": {
+    "@axe-core/playwright": "^4.11.3",
     "@eslint/eslintrc": "^3.3.5",
     "@hookform/devtools": "^4.4.0",
     "@next/bundle-analyzer": "^16.2.6",