feat(app): add Korean (ko) translation for the dashboard (closes #117)

[dchaudhari7177]

Closes #117.

Adds a complete ko catalog, the "ko" member of the Language union, ko in the readSavedLanguage allowlist (so a saved preference survives a reload), and a KO option in the language switcher.

Completeness, checked rather than eyeballed

All 103 catalog keys are translated. Verified programmatically against the en catalog:

• missing in ko: none
• extra in ko: none
• {placeholder} parity: no mismatches — every {id}, {amount}, {token}, {count}, {total}, {pct}, {bps}, {address}, {controller} matches its English counterpart

That last check matters more than it looks: t() falls back to the raw key, not to English, when a key is missing —

let text = dict[key as keyof typeof dict] || key;

— so a partial catalog renders identifiers like sharesTotalWarn straight into the UI rather than degrading to English. A dropped placeholder would likewise silently lose the interpolated value.

Translation notes

• Korean has no plural inflection for these strings, so counts read naturally with the interpolated number (수취인 {count}명).
• Domain terms use the forms common in Korean crypto UIs: 분할 (split), 에스크로 (escrow), 트러스트라인 (trustline), 베이시스 포인트 (basis points), 테스트넷 (testnet).
• Product names (Freighter, GitHub, friendbot, XLM, CSV, bps) are left untranslated.

Verification

• npx vitest run src/lib/i18n.test.tsx — 12 passed
• npm run build — 10 TypeScript errors, identical on pristine main (git stash): all in StreamsCard.tsx / lib/tributary.ts against tributary-sdk, because the SDK workspace isn't built in this checkout. This change adds zero new errors.
• app/package-lock.json was touched by my local npm install; deliberately not committed.

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