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/zh-CN.json

@@ -626,7 +626,13 @@
       "reasoningModel": "推理模型（thinking）",
       "haikuDefaultModel": "Haiku 默认模型",
       "sonnetDefaultModel": "Sonnet 默认模型",
-      "opusDefaultModel": "Opus 默认模型"
+      "opusDefaultModel": "Opus 默认模型",
+      "effortLevel": "推理级别",
+      "effortLevelDefault": "默认级别",
+      "effortLevel_low": "低",
+      "effortLevel_medium": "中",
+      "effortLevel_high": "高",
+      "effortLevelMax": "最高（仅 Opus 支持）"
     },
     "dialogs": {
       "confirmDeleteProvider": "确认删除 Provider {providerId}？",