feat(i18n-ko): desktop slice 2 — remaining settings/conversation/artifact/browser/mcp/plan-mode

## Problem

Remaining Desktop domains still fall back to English in `ko`: conversation, artifacts, browser, MCP, plan mode, and the rest of `settings-*`.

## Desired outcome

Add `ko` entries via `UiCatalog` for:

- `artifact-copy.ts`, `browser-copy.ts`, `conversation-copy.ts`, `external-session-import-copy.ts`
- `mcp-copy.ts`, `plan-mode-copy.ts`
- `settings-bot-copy.ts`, `settings-daily-review-copy.ts`, `settings-data-copy.ts`, `settings-health-copy.ts`, `settings-memory-copy.ts`, `settings-navigation-copy.ts`, `settings-projects-copy.ts`, `settings-provider-copy.ts`, `settings-shared-copy.ts`, `settings-subagents-copy.ts`, `settings-tasks-copy.ts`, `settings-test-result-copy.ts`, `settings-usage-copy.ts`, `settings-web-search-copy.ts`

Follows #3853 coverage for `zh-TW`.

## Alternatives or workarounds

Leave these domains in English.

## Acceptance criteria

- [ ] All listed catalogs provide `ko`; no untranslated fallback where catalog exists
- [ ] Typecheck fails if a new key is added without `ko` entry (`UiCatalog`)
- [ ] `npm --workspace @maka/ui test` / `@maka/core` related suites green
- [ ] Screenshots for representative surfaces (conversation, plan mode)

Parent: #3974

Start by comparing the zh-TW coverage in #3853 and inspect UiCatalog usage in the listed artifact, browser, conversation, MCP, plan-mode, and settings catalog files. Add the missing ko entries across all named catalogs, then run the @maka/ui and related @maka/core test suites and typecheck. Done means no catalog fallback remains, type safety covers new keys, and representative conversation and plan-mode screenshots are provided.

Written by the indexing model from the issue text.