feat(core-ui): add CookieConsentBanner headless component

Implements the EU-compliant cookie consent banner with:
- modal + banner variants, CNIL equal-prominence Reject/Accept buttons
- granular category toggles (essential non-toggleable)
- __consent_state cookie management (SameSite=Lax, Secure, 1-yr, _v:1)
- render-prop overrides: renderHeader, renderCategoryRow, renderActions
- useConsent() integration when ConsentProvider is present
- CookieConsentBannerLoader SSR-safe wrapper
- RTL behavioral tests: Reject All, Save Selected, ESC=Reject, focus-trap
- Storybook stories for modal, banner, render-prop, and a11y tab demo
- jsdom configured with HTTPS origin for Secure cookie testing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-ui/package.json

@@ -14,6 +14,7 @@
     "test": "vitest run --passWithNoTests"
   },
   "dependencies": {
+    "@repo/core-consent": "workspace:*",
     "clsx": "^2.1.1",
     "react": "^19.0.0",
     "tailwind-merge": "^3.0.0"