feat(i18n): en/ko localization with dictionary + cookie-driven provider

[sigco3111]

Summary

This PR introduces full English + Korean localization for GitFut without
changing the visual identity of any surface.

• Translation source-of-truth: lib/i18n/dict/{en,ko}.ts — every user-visible
  string (scoring archetypes, playstyle names, metric labels, style and
  workRate reasons, scout form copy, how-it-works modal, duel view,
  error/404 screens, country names) lives in a typed dictionary.
• Cookie-driven provider: LocaleProvider reads the gitfut_locale cookie on
  the server (so the first paint is correctly localized) and writes it on
  the client when the user toggles. reflects the active locale.
• OG cards / JSON API: locked to EN by passing locale="en" to buildCard()
  — social cards carry the brand read, not the viewer's locale.
• Drift detection: tests/i18n.test.ts asserts every key in en exists in ko
  (and vice versa); adding a key to one without the other now fails CI.

What changed

• New lib/i18n/ directory (8 modules, ~700 LOC): locale negotiation,
  dictionary loader, translator API (t("...", locale, params), typed
  helpers for archetype/playstyle/metric/duel stat-row/duel receipt/country
  name), server resolver, client cookie helpers, hooks.
• New components/LocaleToggle.tsx mounted in the AppShell top-right corner
  next to the Star button.
• Scoring engine now accepts a locale parameter across buildCard,
  derivePlaystyles, deriveSkillMoves, deriveWeakFoot, deriveWorkRate,
  deriveStyle, deriveMetrics. Tests stay identical (default locale is EN).
• lib/duel.ts (computeDuel) now takes a locale so stat-row and receipt
  labels localize; lib/og/renderCard keeps EN because OG cards are brand read.
• lib/countries.ts is left untouched (auto-generated); t.countryName(code,
  locale) reads from the dictionary with EN fallback.
• 250-country dictionary is identical in shape across locales (mirrored
  keys) — KO dictionary overrides priority subset (Korea, Japan, USA, WC26
  hosts, EU neighbours, etc.) and falls back to EN for the rest.

Tested

tests/i18n.test.ts — 19 new tests covering dictionary loading, fallback
for unknown locale, key-set parity, locale negotiation (Accept-Language
parsing, quality factors, region stripping), isLocale / localeFromCookie
guards, t.stat / t.metric / t.style / t.playstyle / t.workRate_reason /
t.attribute.skillMoves / t.attribute.weakFoot, @locked key prefix (always
returns EN), formatCount / formatInt accepting the locale.

npm test → 296/296 passing. npx tsc --noEmit → 0 errors.

Notes

• I leaned on the project's existing single-source-of-truth patterns
  (METRIC_LABELS, FINISH_LABELS) rather than introducing a new i18n library.
  The translator is plain TypeScript so there's no new dependency.
• The footer credit, mascot SVG, and "OFFSIDE" tier art are styled English
  brand reads that don't localize — left as-is.
• HowItWorksModal.laws array got its bullets/laws translated (3 entries +
  hero + reads section + ladder labels).