Record externally completed agent config imports (#34981)

## Why

Clients that complete an external agent config import outside the app server need a way to include the result in import history.

## What changed

- Add `externalAgentConfig/import/recordHistory` to persist completed item results and return a generated import ID.
- Store the optional provider ID for regular imports and expose it when reading import history.
- Update the generated JSON and TypeScript protocol schemas for the new request, response, and history field.

## Testing

- Cover recording and reading an externally completed import through the app-server protocol.
- Cover provider ID persistence and updates in the state runtime.

GitOrigin-RevId: 935401e899ec9eeb38f54c182e45a16642411deb

codex-rs/app-server/src/external_agent_migration/protocol.rs

@@ -210,6 +210,7 @@ pub(super) fn protocol_import_history(
 
     Ok(ExternalAgentConfigImportHistory {
         import_id: record.import_id,
+        provider_id: record.provider_id,
         completed_at_ms: record.completed_at_ms,
         successes,
         failures,