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/es.json

@@ -626,7 +626,13 @@
       "reasoningModel": "Modelo de razonamiento (thinking)",
       "haikuDefaultModel": "Modelo Haiku predeterminado",
       "sonnetDefaultModel": "Modelo Sonnet predeterminado",
-      "opusDefaultModel": "Modelo Opus predeterminado"
+      "opusDefaultModel": "Modelo Opus predeterminado",
+      "effortLevel": "Nivel de razonamiento",
+      "effortLevelDefault": "Nivel predeterminado",
+      "effortLevel_low": "Bajo",
+      "effortLevel_medium": "Medio",
+      "effortLevel_high": "Alto",
+      "effortLevelMax": "Máximo (solo Opus)"
     },
     "dialogs": {
       "confirmDeleteProvider": "¿Eliminar proveedor {providerId}?",