wpa_supplicant: Reuse existing networks and preserve saved ones on connect

Connect() called AddNetwork unconditionally, creating duplicate entries for
the same SSID, and SelectNetwork's side-effect of disabling all other
networks was being persisted by SaveConfig — making previously saved
networks appear erased. Disconnect() also removed the current network from
the config. Now reuse an existing network entry when the SSID matches,
re-enable other networks after SelectNetwork, and keep entries on
disconnect.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/wifi/wpasupplicant/network.go

@@ -1,6 +1,8 @@
 package wpasupplicant
 
 import (
+	"strings"
+
 	"github.com/godbus/dbus/v5"
 )
 
@@ -39,3 +41,25 @@ func (n *Network) GetProperties() (map[string]dbus.Variant, error) {
 
 	return props, nil
 }
+
+// GetSSID returns the configured SSID, stripping the wrapping quotes
+// that wpa_supplicant stores around string-form SSIDs.
+func (n *Network) GetSSID() (string, error) {
+	props, err := n.GetProperties()
+	if err != nil {
+		return "", err
+	}
+
+	ssidVariant, ok := props["ssid"]
+	if !ok {
+		return "", nil
+	}
+
+	ssid, ok := ssidVariant.Value().(string)
+	if !ok {
+		return "", nil
+	}
+
+	// wpa_supplicant returns quoted SSIDs like "MyNetwork"
+	return strings.Trim(ssid, `"`), nil
+}