wifi: omit empty info snapshot and tidy up

- 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

agent/wifi/README.md

@@ -1,47 +1,11 @@
 # Connected Wi-Fi signal
 
-Each default-interval poll reports a snapshot of connected station interfaces
-in `info.wifi`. Map keys identify interfaces, not networks. `s` is optional SSID
-metadata; `r` is nullable native RSSI in dBm. Quality percentages are never
-converted to dBm. An associated interface without an accessible RSSI still
-appears with an unavailable signal. No scans or network changes occur.
-`stats.wf` stores only available RSSI values (integer dBm) keyed by interface.
-Real-time requests reuse the last snapshot instead of collecting again.
+Reports connected station interfaces only (no scans). `info.wf` holds the current
+snapshot keyed by interface (`s` SSID, `r` RSSI in dBm when available);
+`stats.wf` stores available RSSI as integer dBm. Collected on the default
+interval only; real-time requests reuse the last snapshot.
 
-The hub panel gates exclusively on current `systems.info.wifi` and system `up`
-status, independently of the selected historical period. Empty/null snapshots
-clear it. Historical averages use only available readings per interface; gaps
-are not zero signal. Interface colors and keys remain stable on reconnect.
-
-## Platforms
-
-- Linux: native nl80211 through `github.com/mdlayher/wifi`, compiled into the
-  static agent, including scratch and all other agent images. No `iw`, shared
-  libraries, extra capabilities, or external helper required. Host network
-  namespace access (Docker `network_mode: host`) is necessary to see host Wi-Fi.
-  Only managed station interfaces with explicit associated BSS status appear.
-  Kernel BSS cache reads do not trigger scans; station statistics supply native
-  RSSI matched to the associated AP. Denied/missing station statistics retain
-  association with unavailable RSSI, never substitute stale scan-cache signal.
-  Missing nl80211/driver support or denied association reads yield no readings.
-  A single two-second socket deadline bounds enumeration and interface queries
-  after opening the client. The library's initial nl80211 family discovery is
-  synchronous and does not expose a deadline.
-- macOS: system `osascript` uses public CoreWLAN via JXA. Station mode proves
-  association; RSSI and optional SSID are read independently. No private airport
-  binary, elevated command or compiled helper required. Privacy settings may
-  redact SSIDs. The subprocess has a two-second deadline.
-- Windows: native WLAN API, interface GUID identity, connected interface state,
-  optional current-connection SSID and native RSSI query. No localized `netsh`
-  parsing. Missing WLAN service/API yields no readings; denied SSID/RSSI query
-  leaves a connected interface with missing metadata/signal. Non-UTF-8 raw
-  SSIDs are omitted so they cannot invalidate CBOR text in the agent response.
-  Native synchronous WLAN calls cannot be interrupted by the Go deadline.
-- FreeBSD and other platforms: unsupported, empty snapshot. No approximation
-  from ifconfig quality and no stale data retained.
-
-Collectors retry each default-interval poll, allowing interfaces and capabilities to appear
-without an agent restart. Standard agent response caching still applies. Existing
-hub record JSON storage requires no database schema migration. Older agents
-without the field keep the panel hidden. Native macOS/Windows runtime checks and
-real adapter testing are still required; cross compilation is not hardware proof.
+- Linux: nl80211 via `github.com/mdlayher/wifi`. Docker needs `network_mode: host`.
+- macOS: CoreWLAN via `osascript` (JXA). SSID may be redacted by privacy settings.
+- Windows: native WLAN API, keyed by interface GUID.
+- Other platforms: unsupported.

agent/wifi/wifi.go

@@ -5,23 +5,12 @@ package wifi
 import (
 	"context"
 	"math"
-	"os"
-	"os/exec"
 	"time"
 	"unicode/utf8"
 
 	"github.com/henrygd/beszel/internal/entities/system"
 )
 
-type commandRunner func(context.Context, string, ...string) ([]byte, error)
-
-func run(ctx context.Context, name string, args ...string) ([]byte, error) {
-	cmd := exec.CommandContext(ctx, name, args...)
-	cmd.Env = append(os.Environ(), "LC_ALL=C", "LANG=C")
-	cmd.WaitDelay = 100 * time.Millisecond
-	return cmd.Output()
-}
-
 // validSSID omits non-UTF-8 SSIDs: 802.11 permits arbitrary octets, but CBOR
 // text strings require UTF-8. Metadata must never invalidate the whole response.
 func validSSID(ssid string) string {

agent/wifi/wifi_darwin.go

@@ -5,6 +5,9 @@ package wifi
 import (
 	"context"
 	"encoding/json"
+	"os"
+	"os/exec"
+	"time"
 
 	"github.com/henrygd/beszel/internal/entities/system"
 )
@@ -31,7 +34,10 @@ if (interfaces) {
 JSON.stringify(result);`
 
 func collect(ctx context.Context) map[string]system.WiFi {
-	output, err := run(ctx, "/usr/bin/osascript", "-l", "JavaScript", "-e", coreWLANScript)
+	cmd := exec.CommandContext(ctx, "/usr/bin/osascript", "-l", "JavaScript", "-e", coreWLANScript)
+	cmd.Env = append(os.Environ(), "LC_ALL=C", "LANG=C")
+	cmd.WaitDelay = 100 * time.Millisecond
+	output, err := cmd.Output()
 	if err != nil {
 		return nil
 	}