feat: improve replay workflow and viewer UI

Co-Authored-By: Claude Fable 5 <[email protected]>

backend/config.py

@@ -17,6 +17,7 @@ class Settings(BaseSettings):
     media_origin_api_port: int = 9997
     media_origin_hls_port: int = 8888
     replay_media_dir: str = str(APP_DIR.parent / "media")
+    hls_runtime_dir: str = str(APP_DIR.parent / "runtime" / "hls")
     hls_segment_seconds: int = 4
 
     edge_nodes: list[dict] = [