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/value_objects/mod.rs

@@ -3,9 +3,11 @@ pub mod channel;
 pub mod ids;
 pub mod scheduling;
 pub mod search;
+pub mod streaming;
 
 pub use auth::*;
 pub use channel::*;
 pub use ids::*;
 pub use scheduling::*;
 pub use search::*;
+pub use streaming::*;

crates/domain/src/value_objects/streaming.rs

@@ -0,0 +1,8 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum SourceUri {
+    NetworkUrl { url: String },
+    FilePath { path: String },
+}