Expose workspace plugin publish capability (#35254)

## What changed

- Add nullable `canPublishToWorkspace` metadata to plugin share contexts and `plugin/share/save` responses.
- Preserve the remote capability through catalog parsing and app-server responses so clients can decide whether to offer workspace-directory publishing.
- Document that clients should fail closed when the capability is unavailable.

## Testing

- Cover remote catalog parsing, share-save response propagation, and protocol serialization.

GitOrigin-RevId: b0346b3b330169838f800dfdf21dfa5db1a47f4d

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

@@ -1045,6 +1045,7 @@ async fn plugin_detail_popup_shows_local_share_context_as_read_only_snapshot() {
             creator_account_user_id: None,
             creator_name: Some("Test User".to_string()),
             share_principals: None,
+            can_publish_to_workspace: None,
         }),
         ..plugins_test_summary(
             "plugin-docs",
@@ -1326,6 +1327,7 @@ async fn plugins_popup_remote_detail_tracks_physical_and_policy_install_state()
             creator_account_user_id: None,
             creator_name: None,
             share_principals: None,
+            can_publish_to_workspace: None,
         }),
         ..plugins_test_summary(
             "plugin-docs",