refactor: replace get_stream_url with get_source_uri per ADR-0002

Providers now expose a source URI (for FFmpeg) instead of a
viewer-facing stream URL. Playout Service will own transcoding.

- Add SourceUri value object (NetworkUrl | FilePath)
- Remove StreamQuality, StreamingProtocol from domain
- Simplify ProviderCapabilities (drop streaming_protocol, transcode)
- Jellyfin: return static direct stream URL
- Local files: return absolute file path
- Rename use case get_stream_url -> get_source
- Stream endpoint returns JSON SourceUri instead of 307 redirect

crates/domain/src/ports/mod.rs

@@ -17,7 +17,6 @@ pub use events::{DomainEvent, EventConsumer, EventEnvelope, EventHandler, EventP
 pub use library::{LibraryCommand, LibraryQuery, LibrarySyncAdapter};
 pub use media::{
     Collection, IMediaProvider, IProviderRegistry, ProviderCapabilities, SeriesSummary,
-    StreamQuality, StreamingProtocol,
 };
 pub use provider_config::{ProviderConfigCommand, ProviderConfigQuery};
 pub use schedule::{ScheduleCommand, ScheduleQuery};