fix(session): 控制连接断开后自动停播

[ByteColtX]

Summary

• propagate RTSP keepalive failures from the control connection into PlaybackSession
• stop capture automatically in the CLI and tray polling loops when the control channel drops
• add a regression test that simulates a keepalive failure and verifies the session surfaces it

Testing

• cargo fmt --check
• cargo test
• cargo clippy --workspace --all-targets -- -D warnings