## What changed
Allow connector-wide app settings under `plugins.<plugin>.apps.<connector>` for plugins enabled by configuration. Merge these settings field by field, giving earlier plugin names precedence and applying explicit top-level `apps` fields last. Ignore nested `_default` settings.
Expose the merged app settings and their field origins through the config API. Keep app policy changes from invalidating the loaded-plugin cache.
## Testing
Add coverage for plugin enablement, merge precedence, field origins, config API output, cache reuse, and disabling an app through plugin configuration during explicit plugin mentions.
GitOrigin-RevId: a275319815915dc618ee606b10e0844248dbccb5