Footer and legal-sidebar labels are hardcoded English

`LandingFooter.tsx` uses `useFormatMessage` for everything except the legal links — hardcoded twice (desktop `legalLinks` array at :52-57 and duplicated inline in the mobile grid at :277-282). `LegalPageLayout.tsx:25-35` hardcodes all 9 sidebar labels. No corresponding keys exist in any locale file.

Scope deliberately excludes translating the legal page bodies (that's a legal/product decision — many orgs keep legal text English-only on purpose). The labels-only fix: add `component.landing.footer.legal.*` + `component.legal_page.sidebar.*` keys (all 6 locales) and replace the three hardcoded arrays with `l(...)` calls.