fix: keep physical local playback outside Gelato probes

[ChosenQuill]

Summary

Closes #189.

SyncStreams copies the Stremio provider ID to a primary local item. Playback then uses IsGelato(), which treats that metadata ID as Gelato playback ownership and can send the physical local source through Gelato's probe path.

This change keeps the existing metadata behavior but uses playback-specific ownership:

• Gelato stream items are identified by the existing gelato-stream tag.
• Inserted Gelato items are identified by their existing gelato:// path.
• Physical local items delegate to Jellyfin when mixed libraries are disabled.
• With mixed libraries enabled, a selected physical local owner also delegates to Jellyfin; selected Gelato streams keep the existing playback path.

No Gelato stream protocol, probing, stubbing, user resolution, or CI behavior is changed.

Validation

• dotnet build Gelato.sln --configuration Release: succeeded with 0 errors.
• dotnet format Gelato.sln --verify-no-changes --no-restore: clean.
• The exact submitted commit (2e4412e) was built and deployed on Jellyfin 10.11.11. The reproduced physical local title returned one native File source (IsRemote=false, no stub); its HLS playlist and segment returned HTTP 200, and Jellyfin Web playback advanced.
• A remote Gelato fixture still returned one source with HTTP 200 playback info and advanced in Jellyfin Web.

[Copilot]

Pull request overview

Adjusts Gelato playback ownership detection so that Stremio provider IDs remain metadata-only and no longer force physical local media sources through Gelato’s probing/playback path. This aligns playback routing with the intended semantics of mixed libraries and prevents local filesystem sources from being treated as Gelato-owned after SyncStreams.

Changes:

• Replace provider-ID-based ownership checks with playback-specific ownership (gelato-stream tag or gelato:// path).
• Delegate playback back to Jellyfin when the selected media source resolves to a non-Gelato playback owner.
• Centralize the new ownership rule in IsGelatoPlaybackItem(...) and apply it in both static and playback media source flows.

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