feat: sync current providers to live files after config import

Core Improvements:
- Add sync_current_providers_live command to synchronize in-memory provider
  settings to corresponding live files (~/.claude/settings.json or ~/.codex/auth.json)
- Introduce partial-success state to distinguish between 'import succeeded
  but sync failed' scenario, providing clear user feedback
- Remove unused skip_live_backfill parameter from switch_provider command
- Separate responsibilities: backend handles import/backup, frontend handles
  sync/error presentation

Technical Details:
- Codex: sync auth.json + config.toml with MCP configuration
- Claude: sync settings.json
- Bidirectional sync: read back after write to update in-memory settings_config
- Full i18n support (English and Chinese)
- Graceful handling when no current provider is active

Affected Files:
- Backend: import_export.rs, commands.rs, lib.rs
- Frontend: useImportExport.ts, ImportExportSection.tsx, settings.ts
- i18n: en.json, zh.json

This ensures SSOT (Single Source of Truth) consistency between config.json
and live configuration files after import operations.

src/components/settings/ImportExportSection.tsx

@@ -167,6 +167,20 @@ function ImportStatusMessage({
     );
   }
 
+  if (status === "partial-success") {
+    return (
+      <div
+        className={`${baseClass} border-yellow-200 bg-yellow-100/70 text-yellow-700`}
+      >
+        <AlertCircle className="mt-0.5 h-4 w-4" />
+        <div className="space-y-1">
+          <p className="font-medium">{t("settings.importPartialSuccess")}</p>
+          <p>{t("settings.importPartialHint")}</p>
+        </div>
+      </div>
+    );
+  }
+
   const message = errorMessage || t("settings.importFailed");
 
   return (