app: fetch config via configUrl from manifest instead of provider.getAppConfig

In `packages/modules/app/src/app/flows.ts`, `handleFetchConfig` has a TODO suggesting it should use the `configUrl` directly from the manifest rather than going through `provider.getAppConfig(appKey, version)`:

```ts
// TODO - use the configUrl directly from the manifest
// fetch config from provider
const subject = from(provider.getAppConfig(payload.appKey, payload.build?.version)).pipe(
```

Start in packages/modules/app/src/app/flows.ts at handleFetchConfig and trace how the manifest and its configUrl are available alongside the current provider.getAppConfig call. Done means the flow fetches configuration from the manifest's configUrl instead of provider.getAppConfig(appKey, version), while preserving the surrounding config-fetch behavior.

Written by the indexing model from the issue text.