feat(01-02): implement capture package with OpenCapture, ListInterfaces, StartCapture

- ListInterfaces uses net.Interfaces() stdlib (no pcap dependency for listing)
- OpenCapture wraps packetcap/go-pcap with platform-specific permission error handling
- StartCapture uses buffered channel (512) with atomic drop counter
- Dynamic link type detection via layers.LinkType(handle.LinkType())
- Linux error shows setcap cap_net_raw+ep hint; macOS shows sudo hint
- Add github.com/packetcap/go-pcap v0.0.0-20251215 to go.mod

go.sum

@@ -1,2 +1,18 @@
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