Allow opening PCAP files with Sniffnet from the OS

[m-altaifi]

Summary

• adds a positional PCAP file argument for file-open launches
• registers PCAP file associations in Linux, macOS, and Windows packaging
• forwards macOS file-open arguments through the privilege wrapper
• keeps adapter startup explicit by making PCAP_FILE conflict with --adapter

Testing

• cargo fmt --check
• cargo check
• git diff --check
• parsed resources/packaging/macos/Info.plist as XML
• parsed resources/packaging/windows/setup.wxs as XML
• cargo test cli::tests - blocked locally by missing wpcap.lib
• verified opening a .pcap file from the OS launches Sniffnet
• verified regular in-app PCAP import still works

Fixes #1288

[GyulyVGC]

Thanks!
I'll look into this when I have some time.