feat: Add plugin share access controls (#21124)

Extends `plugin/share/save` to accept optional discoverability and
shareTargets while uploading plugin contents, and adds
`plugin/share/updateTargets` for share-only target updates without
re-uploading.

codex-rs/app-server/src/message_processor.rs

@@ -1087,6 +1087,11 @@ impl MessageProcessor {
             ClientRequest::PluginShareSave { params, .. } => {
                 self.plugin_processor.plugin_share_save(params).await
             }
+            ClientRequest::PluginShareUpdateTargets { params, .. } => {
+                self.plugin_processor
+                    .plugin_share_update_targets(params)
+                    .await
+            }
             ClientRequest::PluginShareList { params, .. } => {
                 self.plugin_processor.plugin_share_list(params).await
             }