feat(dashboard): add Korean (ko) translation

[moduvoice]

Motivation

This adds Korean (ko) translation support — to help Korean-speaking users use this
open-source project more comfortably in their own language.
(한국 사람들의 오픈소스 이용에 도움이 되게 하기 위해서 한글화 작업을 하였습니다.)

Changes

• Added a ko.ts locale file next to every existing en.ts/zh.ts pair: dashboard/src/common/locales/ and all 9 feature namespaces (api-keys, auth, databases, keyvalue, logs, metrics, services, team, usage, workspaces) — 592 keys total, full parity with en, placeholders ({name}, {email}, etc.) preserved exactly.
• Registered ko in SUPPORTED_LANGUAGES / LANGUAGE_NAMES (src/i18n/config.ts) and wired its imports into the en/zh/ko resource aggregation in src/i18n/index.ts, following the existing "Adding a language" recipe.
• Extended src/i18n/__tests__/locale-parity.test.ts to also assert en/ko key parity for the namespaces it already covers (common, auth, metrics, services).
• description fields (translator-facing notes, not shown to users) were left in English, matching the existing zh.ts convention.

Testing

• yarn test — all 93 test files / 573 tests pass, including the extended locale-parity suite.
• yarn typecheck and yarn lint — clean, no errors.
• yarn build — production build succeeds.
• yarn prettier --check — all new/changed files pass formatting.
• Ran a standalone key-parity + placeholder-parity script across all 10 namespace pairs (en vs ko) to confirm no key drift beyond what the vitest suite already covers.