feat(i18n-ko): native surfaces and E2E fixtures

[scs0209]

Summary

Wire ko through core locale resolution, desktop native surfaces, and E2E fixtures. This follows the same pattern as #3853 (zh-TW): Korean copy for startup/quit/boot dialogs, diagnostics, notifications, permission overlay, and related main-process fallbacks; E2E fixture flags accept ko / ko-kr without the toLowerCase regression fixed for Chinese locales in #3853 review.

Renderer UiCatalog types require a ko key once ko is in UI_LOCALES. Catalogs outside the #3977–#3979 renderer slices use English stubs for now; session-collaboration-copy includes a real KO block.

Review note: This branch stacks on feat/zh-tw-locale (#3853). GitHub cannot target AcerYue0:feat/zh-tw-locale as the PR base on apache/maka, so the PR currently targets main and includes #3853 commits in the diff. Do not merge until #3853 lands. To review only the Korean work, use:
AcerYue0:feat/zh-tw-locale...scs0209:feat/i18n-ko-native-e2e-3980

Fixes #3980

Verification

• npm run build:test — pass
• node --test packages/core/dist/__tests__/ui-locale.test.js — pass
• node --test apps/desktop/dist/main/__tests__/e2e-fixture-locale.test.js — pass
• Playwright E2E (ko-locale.spec.ts) — not run locally (dev server not started)
• npm run lint / npm run format:check — not run for the full workspace

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Cursor — implementation, translation stubs, tests, and PR text. The update(i18n-ko): session-collaboration… commit includes a Generated-by: Cursor trailer.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No