Phase 1: Infrastructure setup - Install next-intl and create basic i18n structure

- Install next-intl package
- Create LanguageProvider hook with localStorage persistence
- Create IntlProvider component for next-intl integration
- Create Providers wrapper component
- Update layout.tsx to include providers and set default lang to 'es'
- Create initial translation files (common.json) for es, en, ca
- Fix pre-existing TypeScript errors in various pages

All tests passing, build successful.

frontend/app/hooks/useTranslation.ts

@@ -0,0 +1,8 @@
+"use client";
+
+import { useTranslations as useNextIntlTranslations } from "next-intl";
+
+export function useTranslation(namespace?: string) {
+  const t = useNextIntlTranslations(namespace);
+  return t;
+}