Add analytics status controls - #276

Summary

• Add visible analytics status and opt-out controls to Local Data Controls on the Privacy page.
• Keep analytics disabled by default while storing a browser-local opt-out preference for future provider-enabled deployments.
• Document allowed analytics events, allowed coarse fields, and forbidden sensitive fields directly in UI.
• Add unit and component coverage for analytics preference behavior and visible controls.

Validation

• npm test -- tests/unit/analytics-utils.test.ts tests/component/privacy-page.test.tsx tests/guards/analytics-taxonomy.test.ts tests/component/representative-a11y-axe.test.tsx
• npm run check:i18n
• npm run check:i18n-qa
• npm run check:types
• npm run check:analytics-taxonomy
• npm run check:sitemap-lastmod
• npm run lint (passes with existing coverage/block-navigation.js warning)

Closes #258