hostd: desktop notifications on match

[dougborg]

Summary

Show a desktop notification when hostd detects a surveillance device match, using native OS notification APIs.

Implementation

• Use notify-rust crate (supports macOS, Linux, Windows)
• Add --notify CLI flag to enable
• Show: device type, name/MAC, matched rule/signature, RSSI
• Rate-limit notifications (e.g., one per device per 60s) to avoid spam
• Optional: sound alert

Related

• arch: multi-platform architecture — shared core, multiple runtimes #17 — multi-platform architecture