Add per-login MCP OAuth client registration selection (#38052)

## What changed

- Add `--oauth-client-registration` with `auto` and `dcr` choices to `codex mcp add` and `codex mcp login`.
- Add the equivalent optional `clientRegistration` field to `mcpServer/oauth/login` and the generated protocol schemas.
- Keep automatic dynamic client registration as the default, prefer a configured OAuth client ID when present, and apply the selection only to the current login without persisting it in MCP configuration.

## Testing

- Cover dynamic registration and configured-client OAuth flows through the app server.
- Verify the CLI does not persist the per-login registration choice.

GitOrigin-RevId: 653a4a1054ff43c2c5d52ae863b6a96d21692a53

codex-rs/app-server/src/request_processors/mcp_processor.rs

@@ -118,9 +118,14 @@ impl McpRequestProcessor {
         let McpServerOauthLoginParams {
             name,
             thread_id,
+            client_registration,
             scopes,
             timeout_secs,
         } = params;
+        let client_registration = match client_registration.unwrap_or_default() {
+            McpServerOauthClientRegistration::Auto => McpOAuthClientRegistration::Auto,
+            McpServerOauthClientRegistration::Dcr => McpOAuthClientRegistration::Dcr,
+        };
 
         let auth = self.auth_manager.auth().await;
         let (mcp_config, runtime_context) = match thread_id.as_deref() {
@@ -201,6 +206,7 @@ impl McpRequestProcessor {
             env_http_headers,
             &resolved_scopes.scopes,
             server.oauth_client_id(),
+            client_registration,
             server.oauth_resource.as_deref(),
             timeout_secs,
             mcp_config.mcp_oauth_callback_port,