feat(i18n-ko): desktop slice 1 — settings-preferences/onboarding/shell/permissions

## Problem

Desktop Settings / Onboarding / Shell surfaces have no `ko` catalog. Korean users see English fallback for the most visible entry points (language selector, onboarding, shell chrome, permissions).

## Desired outcome

Add `ko` entries via `UiCatalog` for:

- `settings-preferences-copy.ts` (including language selector labels: Follow system / 한국어 / English / 中文)
- `onboarding-copy.ts`
- `shell-copy.ts` + `shell-remaining-copy.ts`
- `permission-center-copy.ts`

Follows domain-owned catalog pattern in #2672; content lives next to its UI, as in #3853.

## Alternatives or workarounds

Leave these surfaces in English for `ko`.

## Scope

Only the four domains above. No global catalog, no framework change. Other `settings-*` / `conversation` / `artifact` / `browser` covered in slice 2.

## Acceptance criteria

- [ ] `ko` selected → the four domains render Korean, `en` shows no Korean
- [ ] `auto` + `ko-KR` system → `ko` (via parent #3974 core change)
- [ ] `npm run lint && npm run format:check && npm run build && npm run typecheck` green
- [ ] Unit tests: `settings-preferences-copy.test.ts` etc. cover `ko`
- [ ] Screenshots: Settings at 1280 + 430 for `en`/`ko` (as in #3853 / #3970)

Parent: #3974