Screen sharing was not detected by PrivacyService on Niri because:
1. Niri creates the screencast as a Stream/Output/Video node, but
screensharingActive only checked PwNodeType.VideoSource nodes.
2. looksLikeScreencast() only inspected application.name and
node.name, missing Niri's node which has an empty application.name
but identifies itself via media.name (niri-screen-cast-src).
Add Stream/Output/Video to the checked media classes and include
media.name in the screencast heuristic. Also add a forward-compatible
check for NiriService.hasActiveCast for when Niri gains cast tracking
in its IPC.
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>