perf(playout): parallelize playlist validation with dedup and worker pool

backend/playout/start-playout.sh

@@ -17,15 +17,7 @@ file '/app/media/demo2.mp4'
 EOF
 fi
 
-# Run normalization validation using the Go tool
-echo "Validating playlist and enforcing normalization (ADR-001/ADR-003)..."
-if ! /app/playlist-manager -validate "$PLAYLIST_PATH"; then
-  echo "ERROR: Playlist validation failed. Check logs."
-  exit 1
-fi
-
-echo "Playlist validated successfully. Starting continuous HLS playout..."
-
-# Single source of truth: the Go binary runs the full loop (HLS, R2 sync,
-# slate fallback, health server). The shell no longer duplicates the FFmpeg loop.
+# Single source of truth: the Go binary validates the playlist (ADR-001/ADR-003
+# normalization enforcement) and runs the full loop (HLS, R2 sync, slate
+# fallback, health server). Validation runs once inside the binary.
 exec /app/playlist-manager "$PLAYLIST_PATH"