Portuguese translation of the UI #35

Why

The event was in Lisbon, and a lot of the community reads Portuguese first.

What to build

• i18n with a small runtime (for example i18next) and every UI string in apps/web/src/components and pages extracted into message files.
• pt-PT as the first translation.
• A language toggle in the footer (components/layout/site-footer.tsx), persisted with the existing hooks/use-local-storage-state.ts.
• Project descriptions and chat answers are not translated.

Acceptance criteria

• No hardcoded English strings are left in components/ and pages/, enforced by a check that runs in CI.
• Switching the language updates the whole page without a reload.

See CONTRIBUTING.md for conventions.