[frontend] Finish Argilla → Extralit rebrand sweep

[JonnyTran]

Problem

Leftover Argilla / Recognai references across the frontend cause confusion and broken doc links. SDK and server are clean.

Known sites (non-exhaustive — issue should include a fresh grep)

• extralit-frontend/translation/{en,de,ja}.js — i18n key argillaDatasets
• extralit-frontend/v1/infrastructure/types/environment.ts — argilla: { ... } typing
• extralit-frontend/nuxt.config.ts — link to how-to-configure-argilla-on-huggingface
• extralit-frontend/v1/.../useShareViewModel.ts — https://argilla.imglab-cdn.net/dibt/dibt_v2.png
• extralit-frontend/components/.../DatasetList.vue — i18n key argillaDatasets
• E2E mocks: argilla.span_marker_conll, argilla-other
• Copyright headers across the codebase: "Copyright 2021-present, the Recognai S.L. team"

Approach

1. grep -rni "argilla\|recognai" extralit-frontend/ for the full list.
2. Replace identifiers (i18n keys, type names, URLs) with extralit equivalents.
3. Update copyright headers per project convention.
4. Update any docs links to current Extralit URLs.

Acceptance criteria

• grep -rni "argilla\|recognai" extralit-frontend/ --exclude-dir=node_modules returns no matches except in third-party license notices.
• Frontend builds and tests pass; existing snapshots updated.

[aarab002]

ill take this