store compact RSSI stats and skip real-time collection

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.

internal/entities/system/system.go

@@ -20,7 +20,6 @@ type WiFi struct {
 }
 
 type Stats struct {
-	WiFi           map[string]WiFi     `json:"wifi,omitempty" cbor:"40,keyasint,omitempty"`
 	Cpu            float64             `json:"cpu" cbor:"0,keyasint"`
 	MaxCpu         float64             `json:"cpum,omitempty" cbor:"-"`
 	Mem            float64             `json:"m" cbor:"2,keyasint"`
@@ -64,6 +63,7 @@ type Stats struct {
 	Batteries         map[string]uint8     `json:"bats,omitempty" cbor:"37,keyasint,omitempty"`
 	ZfsPools          map[string]*ZfsPool  `json:"z,omitempty" cbor:"39,keyasint,omitempty"`  // ZFS pool metrics, keyed by pool name
 	DiskIOTotal       [2]uint64            `json:"diot,omitzero" cbor:"38,keyasint,omitzero"` // [total read bytes, total write bytes] cumulative device counters
+	WiFi              map[string]int8      `json:"wf,omitempty" cbor:"40,keyasint,omitempty"` // RSSI dBm keyed by interface; unavailable readings omitted
 
 }
 

internal/entities/system/wifi_test.go

@@ -10,7 +10,10 @@ import (
 func TestWiFiWireSnapshot(t *testing.T) {
 	signal := -55.0
 	for _, wifi := range []map[string]WiFi{nil, {}, {"wlan0": {SSID: "home", Signal: &signal}, "wlan1": {}}} {
-		original := CombinedData{Info: Info{WiFi: wifi}, Stats: Stats{WiFi: wifi}}
+		original := CombinedData{Info: Info{WiFi: wifi}, Stats: Stats{WiFi: make(map[string]int8, len(wifi))}}
+		for id := range wifi {
+			original.Stats.WiFi[id] = -55
+		}
 		encoded, err := cbor.Marshal(original)
 		if err != nil {
 			t.Fatal(err)