Refresh host skill catalogs through world state (#33425)

## Why

Host skills can change after a thread starts. Subsequent turns need the updated
catalog without reinjecting an unchanged catalog on every turn.

## What changed

- Register the host skill provider in app-server and project its catalog through
  a dedicated World State section.
- Render host skills with the existing metadata budget and usage instructions,
  including skill-root aliases when available.
- Suppress the legacy host catalog and contextual fragment when World State owns
  the catalog, while preserving host skills for explicit and shadow selection.

## Testing

Added an app-server test that installs a host skill at runtime and verifies the
catalog updates once and remains stable on the following turn.

GitOrigin-RevId: 4cacc6b2258fc3cab8499fbdf9aa6ab0324ec10d

codex-rs/app-server/src/extensions.rs

@@ -83,7 +83,8 @@ where
         .with_executor_provider(executor_skill_provider)
         .with_orchestrator_provider(Arc::new(
             codex_skills_extension::OrchestratorSkillProvider::new(),
-        ));
+        ))
+        .with_host_provider(Arc::new(codex_skills_extension::HostSkillProvider::new()));
     codex_skills_extension::install_with_providers_and_metrics(
         &mut builder,
         skill_providers,