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-tauri/src/lib.rs

@@ -11,8 +11,8 @@ mod migration;
 mod provider;
 mod settings;
 mod speedtest;
-mod usage_script;
 mod store;
+mod usage_script;
 
 use store::AppState;
 use tauri::{
@@ -509,6 +509,7 @@ pub fn run() {
             import_export::import_config_from_file,
             import_export::save_file_dialog,
             import_export::open_file_dialog,
+            import_export::sync_current_providers_live,
             update_tray_menu,
         ]);
 
@@ -537,4 +538,4 @@ pub fn run() {
             let _ = (app_handle, event);
         }
     });
-}
+}