scraper: fix RealJamVR/PornCornVR cast selector and populate SiteID

[driftwood-archivist]

• Cast links on both realjamvr.com and porncornvr.com are direct children of the "Starring:" block (div.mb-1). The PornCorn branch selector, div.scene-view > a[href^='/actor/'], matched nothing, so the whole cast was silently dropped. Both sites now share a single ForEach on div.mb-1, matching the live template.
• Populate sc.SiteID from the scene's numeric data-id, matching the SceneID = slug-SiteID pattern used by the other scrapers (the live test asserts a non-empty SiteID).
• Document realjamvr/porncornvr live-test targets: both sites run through the same RealJamSite function, so one template change breaks both at once.

Fixes #2289