[apps] Thread structured icon assets through app list (#29889)

## Summary

- Add `iconAssets` and `iconDarkAssets` to the app-list protocol.
- Preserve structured icons through directory merging and the connector,
app-
  server, and TUI boundaries.
- Keep legacy logo URLs unchanged as compatibility fallbacks.
- Update generated protocol schemas and TypeScript types.

codex-rs/app-server-protocol/src/protocol/v2/apps.rs

@@ -83,6 +83,8 @@ pub struct AppInfo {
     pub description: Option<String>,
     pub logo_url: Option<String>,
     pub logo_url_dark: Option<String>,
+    pub icon_assets: Option<HashMap<String, String>>,
+    pub icon_dark_assets: Option<HashMap<String, String>>,
     pub distribution_channel: Option<String>,
     pub branding: Option<AppBranding>,
     pub app_metadata: Option<AppMetadata>,