- Add bpfFilter and readPath global vars with flag registration
- Add deriveOutputPath helper: capture.pcap -> capture.mp3 (D-05)
- run() validates mutual exclusion of --read and -i (D-03)
- run() pre-validates BPF filter via capture.ValidateBPFFilter before capture (CAPT-05)
- runLiveMode: extracts existing live pipeline, passes bpfFilter to StartCapture
- runPcapMode: reads pcap with ReadPcapFile, classifies with timestamps, AggregatePcap, encodes
- Bookend messages: 'Reading <file>...' at start, 'Saved...' at end (D-06)
- --verbose supported in pcap mode via onSnapshot callback (D-07)
- Empty pcap produces clear error with file path (Pitfall 4)