hostd: CLI argument parsing and configuration

[dougborg]

Summary

Add proper CLI argument parsing to hostd using clap, replacing the current hardcoded defaults.

Arguments

• --listen <addr:port> — enable TCP listener
• --log-dir <path> — enable file logging
• --notify — enable desktop notifications
• --rssi <threshold> — minimum RSSI (default: -80)
• --no-ble / --no-wifi — disable specific scan types
• --signatures <path> — load custom signature file (relates to feat: runtime signature loading and update protocol #14)
• --verbose / -v — increase log verbosity
• --json — output structured logs (for systemd journal)

Dependencies

• clap = { version = "4", features = ["derive"] }

Related

• feat: runtime signature loading and update protocol #14 — runtime signature loading
• feat: Linux standalone daemon for direct WiFi/BLE capture #13 — Linux daemon