[codex] Add created-by-me remote plugin marketplace (#28203)

## Summary
- add the `created-by-me-remote` marketplace backed by paginated
`scope=USER` plugin directory and installed-plugin requests
- include USER plugins in installed-plugin caching, bundle sync, and
stale-cache cleanup without client-side discoverability filtering
- expose the marketplace through app-server v2 and regenerate the
protocol schemas

## Testing
- `cargo build -p codex-app-server --bin codex-app-server`
- production-auth `plugin/list` smoke test for `created-by-me-remote`
(returned the expected USER plugin as installed and enabled)
- `just test -p codex-core-plugins` (221 passed)
- `just test -p codex-app-server-protocol` (231 passed)
- `just test -p codex-app-server suite::v2::plugin_list::` (37 passed)
- `just fix -p codex-core-plugins -p codex-app-server-protocol -p
codex-app-server`
- `just fmt`

codex-rs/core/src/plugins/discoverable_tests.rs

@@ -244,7 +244,7 @@ remote_plugin = true
             .all(|plugin| plugin.id != "github@openai-curated-remote")
     );
 
-    for scope in ["GLOBAL", "WORKSPACE"] {
+    for scope in ["GLOBAL", "USER", "WORKSPACE"] {
         Mock::given(method("GET"))
             .and(path("/backend-api/ps/plugins/installed"))
             .and(query_param("scope", scope))