mdlayher/wifi only dumps stations, which some full-MAC drivers (e.g.
out-of-tree Realtek USB) answer with an empty list, leaving RSSI
unavailable. Request the associated BSSID's station directly, as
`iw link` does, and parse it with native.ParseStationInfo.
- Info.WiFi uses json "wf" with omitempty so systems without Wi-Fi no
longer store/broadcast "wifi":null
- move osascript exec into wifi_darwin.go; drop unused commandRunner
- share strongest-connection logic between table cell and sorting
- trim agent/wifi README
Stats.WiFi is now map[string]int8 (json "wf") holding only available
RSSI
readings; SSID and unavailable signals stay in Info.WiFi. Averages are
rounded to whole dBm.
Wi-Fi is collected only on the default 60s interval; real-time requests
reuse the last snapshot to avoid spawning osascript / dumping the BSS
cache every second.
