feat(settings): add reasoning effort level for Claude Code

Add an Effort Level dropdown under the Claude Code model inputs with
options Low / Medium / High / Max (Opus only). The selection writes an
"effortLevel" key at the root of the Claude Code config JSON, and is
removed when the default is chosen. Manual edits to the native JSON
textarea stay in sync with the dropdown.

src/i18n/messages/ko.json

@@ -626,7 +626,13 @@
       "reasoningModel": "추론 모델 (thinking)",
       "haikuDefaultModel": "기본 Haiku 모델",
       "sonnetDefaultModel": "기본 Sonnet 모델",
-      "opusDefaultModel": "기본 Opus 모델"
+      "opusDefaultModel": "기본 Opus 모델",
+      "effortLevel": "추론 수준",
+      "effortLevelDefault": "기본 수준",
+      "effortLevel_low": "낮음",
+      "effortLevel_medium": "중간",
+      "effortLevel_high": "높음",
+      "effortLevelMax": "최고 (Opus만 지원)"
     },
     "dialogs": {
       "confirmDeleteProvider": "Provider {providerId}를 삭제하시겠습니까?",