feat(legal): allow partners to customise Terms of Use and Privacy Policy

[wilfredeveloper]

JIRA

Summary

• Replaces the bundled, build-time !!raw-loader imports of the Terms of Use and Privacy Policy markdown with a runtime fetch driven by a new partner-customisable env var FRONTEND_LEGAL_DOCUMENTS (mirrors the existing logo / asset customisation model).
• Partners can either replace frontend-new/public/legal/{terms-of-use,privacy-policy}.md in their fork (Path A) or point each variant at an absolute URL (Path B). Schema is forward-compatible to Record<Locale, string> for future per-locale documents.
• Renames the LegalDocumentVariant union from "privacy" | "terms" to "privacyPolicy" | "termsOfUse" for consistency with the JSON config. Drops the unused {{appName}} placeholder substitution (zero usages in the bundled docs).

What changed

• Config: new legal.documents namespace in config/default.json; wired through config/inject-config.py (env map + JSON-stringify field).
• IaC: added env-var whitelist entry (iac/templates/env.template), reader (iac/frontend/prepare_frontend.py), and no_cache_paths entries (iac/frontend/deploy_frontend.py).
• Frontend:
  • New legalDocumentsConfig.ts parser (modelled on branding/seoConfig.ts).
  • Rewrote legalDocumentLoader.ts to fetch from the configured URL with a per-variant default title fallback.
  • LegalDocumentPage now async-loads with <Backdrop> while loading and <ErrorPage showRefreshButton /> on failure (mirrors KnowledgeHubDocument).
  • New legal.documentUnavailable translation key added to all 7 locales.
  • Default markdown files moved from src/legal/documents/ to public/legal/.
• Docs: new "Legal Documents Configuration" section in config/CUSTOMIZATION.md (Path A/B, frontmatter contract, non-goal callout for re-consent, forward-compat callout for per-locale).
• Tests: 13 unit tests across legalDocumentsConfig.test.ts, legalDocumentLoader.test.ts, and LegalDocumentPage.test.tsx covering success, loading, fetch failure, missing config, malformed JSON, and frontmatter fallback.

Non-goals

• No backend changes; accepted_tc: datetime semantics preserved. Updates affect only future consents.
• No per-locale legal docs in v1 (schema is additive-extensible).
• No admin-frontend upload UI; the ticket's "upload" requirement is satisfied by the partner-config-at-deploy-time model, consistent with how logos already work.

Test plan

• yarn compile clean
• yarn lint clean
• yarn format:check clean
• yarn test --testPathPattern='src/legal/' — 13/13 pass (full suite not run locally due to OOM risk; CI will cover)
• python3 inject-config.py --config default.json runs clean and writes the expected FRONTEND_LEGAL_DOCUMENTS: btoa(JSON.stringify({...})) into env.js
• Manual QA: visit /terms-of-use and /privacy-policy, confirm rendering with defaults
• Manual QA: edit public/legal/terms-of-use.md, hard-refresh, confirm the change is visible
• Manual QA: temporarily rename the public file to confirm <ErrorPage> shows with refresh button

[irumvanselme]

If thre is no URL, I think it might be a good idea to return the default values instead of throwing an error.

for backward config compatibility.

"documents": {
      "termsOfUse": "/legal/terms-of-use.md",
      "privacyPolicy": "/legal/privacy-policy.md"
    }

What do you think?