Add live group standings tab to the tournament page

[borland667]

Summary

Adds a Groups | Standings | Knockout tab nav on the tournament page and a new Standings tab that mirrors the official FIFA standings layout — one FIFA-style table per group with P / W / D / L / GF / GA / GD / Pts, sorted by points → goal difference → goals for → team name.

The view exposes a Live results vs My picks toggle for signed-in participants. The picks view reuses the same table layout but only populates rank + team name (predictions store finishing order, not score lines).

No schema or API changes are required — Match.homeScore, awayScore, status, and homeLabel/awayLabel are already populated by the results importer.

What changed

• New pure utility src/utils/standings.js
  • computeGroupStandings(group, matches) — derives the 8-column FIFA-style row per team
  • computePredictedGroupStandings(group, prediction) — projects a user's first/second/third onto the same shape
• tests/standings.test.js — 9 unit cases (empty, partial, full, draw, tiebreakers, foreign matches, partial picks)
• src/pages/Tournament.jsx
  • new tab nav (Groups | Standings | Knockout) above the existing structure sections
  • new Standings section: per-group cards with FIFA-style tables and the Live / Picks toggle
  • existing Groups and Knockout sections wrapped in tab-aware conditionals
• src/index.css — design-system styles for the view tabs, the standings toggle, and the per-group standings table (dark + light themes, responsive 1/2/3-column grid matching the groups grid)
• i18n: tournament.knockout, tournament.standingsViewActual, tournament.standingsViewPicks, tournament.standingsPicksNote, tournament.standingsEmpty, and the tournament.standingsTable.* column headers (short + full) added in en / es / pt / it / nl with each language's canonical sports abbreviations (PJ/G/E/P in Spanish, J/V/E/D in Portuguese, PG/V/N/P in Italian, GS/W/G/V in Dutch, P/W/D/L in English).
• Docs: IMPLEMENTATION_STATUS.md and QA_CHECKLIST.md updated to reflect the new view.

Test plan

• npm run verify (lint + db:generate + db:validate + node --test + vite build) — all green locally
• 9 new unit tests cover: all-zero baseline, ignoring unscored matches, mixed W/D/L row math, multi-tiebreaker sort (points → GD → GF → name), goals-for tiebreaker, foreign-group matches dropped, full prediction ranking, missing prediction (alphabetical), partial / unknown prediction ids
• Manual smoke: open seeded World Cup 2026, switch through the three tabs, confirm zeroed standings until results arrive, then re-run npm run import:results and confirm the table updates

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