Combine DomAccess.addScript and loadScript into a unified API

[tobiu]

DomAccess.addScript() and DomAccess.loadScript() currently provide similar functionality but with different implementations and use cases.

addScript is exposed as a remote method, while loadScript is a local helper used by addons.

We should merge these into a single, robust API that:

1. Supports both remote and local usage.
2. Handles both adding the tag and tracking loading state (Promise-based).
3. Standardizes the configuration object.

This is a technical debt cleanup task.

[github-actions]

This issue is stale because it has been open for 90 days with no activity.