[codex] expose remote plugin share URL (#27890)

## Summary

- expose the remote plugin detail endpoint's `share_url` as nullable
`PluginDetail.shareUrl`
- preserve existing `PluginSummary.shareContext` behavior for local and
workspace sharing flows
- regenerate the app-server TypeScript and JSON schema fixtures

## Why

The remote plugin detail response already includes a canonical
`share_url`, but that value was not surfaced by `plugin/read` for global
plugins. Global plugins intentionally have no `shareContext`, so using
that model for the URL would change the semantics consumed by the
existing share modal.

## User impact

Codex clients can use `PluginDetail.shareUrl` for a remote plugin's
copy-link action, including when the plugin is disabled by an
administrator, without changing existing share-modal or ownership
behavior.

## Validation

- `cargo test -p codex-app-server
plugin_read_includes_share_url_for_admin_disabled_remote_plugin`
- `cargo test -p codex-app-server-protocol
typescript_schema_fixtures_match_generated`
- `cargo test -p codex-app-server-protocol
json_schema_fixtures_match_generated`
- `cargo fmt --all`

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

@@ -163,6 +163,7 @@ pub struct RemotePluginDetail {
     pub marketplace_name: String,
     pub marketplace_display_name: String,
     pub summary: RemotePluginSummary,
+    pub share_url: Option<String>,
     pub description: Option<String>,
     pub release_version: Option<String>,
     pub bundle_download_url: Option<String>,
@@ -1048,6 +1049,7 @@ async fn build_remote_plugin_detail(
         marketplace_name,
         marketplace_display_name: scope.marketplace_display_name().to_string(),
         summary: build_remote_plugin_summary(&plugin, installed_plugin.as_ref())?,
+        share_url: plugin.share_url,
         description: non_empty_string(Some(&plugin.release.description)),
         release_version: plugin.release.version,
         bundle_download_url: plugin.release.bundle_download_url,