feat: Expose plugin versions and gate plugin sharing (#22397)

- Adds localVersion to plugin summaries and remoteVersion to share
context, including generated API schemas.
- Hydrates local and remote plugin versions from manifests and remote
release metadata.
- Adds default-on plugin_sharing gate for shared-with-me listing and
plugin/share/save, with disabled-path errors
    and focused coverage.

codex-rs/tui/src/chatwidget/tests/helpers.rs

@@ -1315,6 +1315,7 @@ pub(super) fn plugins_test_summary(
     PluginSummary {
         id: id.to_string(),
         remote_plugin_id: None,
+        local_version: None,
         name: name.to_string(),
         share_context: None,
         source: PluginSource::Local {