feat: let user choose which audiostream to extract

config.toml

@@ -25,6 +25,8 @@ normalize = true
 target_lufs = -14       # -14 streaming, -23 broadcast
 target_tp = -1.0        # true peak limit (dBTP)
 target_lra = 11         # loudness range
+# Audio stream selection: null = prompt interactively, int = use that index, "skip" = no audio
+# stream = null
 
 [sync]
 # Analysis window: null = use full extracted duration; otherwise limit for quick test