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-protocol/src/protocol/common.rs

@@ -628,6 +628,11 @@ client_request_definitions! {
         serialization: global("config"),
         response: v2::PluginShareSaveResponse,
     },
+    PluginShareUpdateTargets => "plugin/share/updateTargets" {
+        params: v2::PluginShareUpdateTargetsParams,
+        serialization: global("config"),
+        response: v2::PluginShareUpdateTargetsResponse,
+    },
     PluginShareList => "plugin/share/list" {
         params: v2::PluginShareListParams,
         serialization: global("config"),